Nonaqueous electrolytic solution and nonaqueous electrolytic solution secondary battery using same

ABSTRACT

The present invention relates to a nonaqueous electrolytic solution for use in a nonaqueous electrolytic solution secondary battery that comprises a negative electrode and a positive electrode capable of storing and releasing metal ions, and a nonaqueous electrolytic solution, wherein the nonaqueous electrolytic solution contains the specific compounds (A) and (B).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 15/719,258, filed onSep. 28, 2017, which is a Continuation of U.S. application Ser. No.13/955,373, filed Jul. 31, 2013, which is a continuation ofPCT/JP2012/052017, filed Jan. 30, 2012, the text of which is herebyincorporated by reference, and claims foreign priority to Japanesepatent application 2011-024873 filed Feb. 8, 2011 and Japanese patentapplication 2011-018561 filed Jan. 31, 2011, the entire contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to nonaqueous electrolytic solutions, andnonaqueous electrolytic solution secondary batteries using same,specifically to nonaqueous electrolytic solutions containing specificcomponents and for use in lithium secondary batteries, and to lithiumsecondary batteries using such nonaqueous electrolytic solutions.

BACKGROUND ART

There has been increasing demands for higher capacity secondarybatteries in response to miniaturization of electronic devices driven byrapidly advancing development in the industry. This has prompteddevelopment of the lithium secondary batteries having higher energydensity than nickel-cadmium batteries and nickel-hydrogen batteries.There has also been repeated effort for improving performance.

Against the background of increasing global challenges such asenvironmental and energy problems, there are high expectations for theapplication of lithium secondary batteries to large power supplies suchas car power supplies and stationary power supplies. However, becausesuch batteries are generally intended for use in environments exposed toambient air, battery characteristics, particularly low-temperaturedischarge characteristics under low-temperature environment such asbelow freezing point are considered important in battery development.Further, because of its use, such batteries are required to have betterlife performance than conventional lithium secondary batteries.

The main components of the lithium secondary batteries are the positiveelectrode, the negative electrode, the separator, and the electrolyticsolution. The electrolytic solution is typically a nonaqueouselectrolytic solution produced by dissolving an electrolyte such asLiPF₆, LiBF₄, LiClO₄, LiCF₃SO₃, LiAsF₆, LiN(CF₃SO₂)₂, and LiCF₃(CF₂)₃SO₃in a nonaqueous solvent such as cyclic carbonate (ethylene carbonate,propylene carbonate, and the like), chain carbonate (dimethyl carbonate,diethyl carbonate, ethylmethyl carbonate, and the like), cyclic ester(γ-butyrolactone, γ-valerolactone, and the like), and chain ester(methyl acetate, methyl propionate, and the like).

There are various studies of nonaqueous solvent and electrolyte toimprove the low-temperature discharge characteristics and the cyclecharacteristics of the lithium secondary batteries. For example, PatentDocument 1 describes using a vinyl ethylene carbonatecompound-containing electrolytic solution to minimize degradation of theelectrolytic solution and produce a battery of excellent storagecharacteristics and cycle characteristics. Patent Document 2 describesusing a propane sultone-containing electrolytic solution to increase therecover capacity after storage.

Patent Document 3 discloses using an electrolytic solution that containsa cyclic sulfonic acid ester having an unsaturated bond to fabricate abattery that can suppress degradation of the electrolytic solution evenunder high-temperature environment.

However, while containing these compounds provides some effect ofimproving storage characteristics and cycle characteristics, they form ahigh-resistance coating on the negative electrode side and lower thelow-temperature discharge characteristics.

In an effort to improve the low-temperature discharge characteristics ofthe lithium secondary batteries, there have been efforts to suppress thereaction resistance of the system in a low-temperature discharge stateby addition of a specific compound.

In Patent Document 4, there is a report of adding a silicone-baseddefoaming agent to the electrolytic solution to improve thelow-temperature discharge capacity.

In Patent Documents 5 to 7, there are reports of suppressing thelow-temperature internal resistance by using a technique whereby asilicon compound having an unsaturated bond is added to the electrolyticsolution.

In Patent Document 8, there is a report of using a negative electrodecontaining Si, Sn, and the like as a main component, and adding anethylene carbonate derivative and a predetermined Si-containing compoundto the electrolytic solution to suppress battery swelling and improvecycle life.

Patent Documents 9 and 10 introduce techniques wherebyhexamethyldisilane is added as an additive to reduce the irreversiblecapacity at the negative electrode, and suppress the degradationreaction of the electrolytic solution at the negative electrode.

In Patent Documents 11 and 12, there are reports of adding a phosphazenederivative to the electrolytic solution to suppress the interfaceresistance of the electrolytic solution and improve low-temperaturedischarge characteristics.

In Patent Documents 13 to 15, there are reports of improvinglow-temperature discharge characteristics by using a technique whereby apredetermined phosphoric acid compound is added to the electrolyticsolution.

CITATION LIST Patent Documents

Patent Document 1: JP-A-2001-006729

Patent Document 2: JP-A-10-050342

Patent Document 3: JP-A-2002-329528

Patent Document 4: JP-A-11-185804

Patent Document 5: JP-A-2002-134169

Patent Document 6: JP-A-2003-173816

Patent Document 7: JP-A-2003-323915

Patent Document 8: US Patent Application 2010/159336

Patent Document 9: JP-A-2010-116475

Patent Document 10: JP-A-2010-9940

Patent Document 11: JP-A-2001-217006

Patent Document 12: JP-A-2002-83628

Patent Document 13: JP-A-2007-141830

Patent Document 14: JP-A-2007-165292

Patent Document 15: JP-A-2010-62164

As described above, despite the efforts to improve low-temperaturedischarge characteristics and cycle characteristics, the results areinsufficient to achieve sufficient battery characteristics, and furtherimprovements are needed.

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

In Patent Documents 5 to 7, a technique is reported whereby a compoundcontaining a predetermined Si—Si bond is added to the electrolyticsolution to improve low-temperature characteristics.

According to Patent Documents 5 to 7, the technique, with the use of asilane compound having an unsaturated bond that easily undergoesself-polymerization, causes a polymerization reaction at the electrodeinterface at the initial stage of a cycle to form a stable coating andthereby suppress an increase of interface resistance associated with thecycle.

However, while the use of a compound that easily undergoesself-polymerization can stabilize the coating, it may form the coatingin excess, which may lead to high resistance at initial use.

With regard to the technique reported in Patent Document 8 whereby apredetermined Si-containing compound is added to the electrolyticsolution, the technique is limited to negative electrodes that containelements such as Si and Sn as a main component. Further, the techniqueis described as involving poor cycle characteristics.

With regard to the technique introduced in Patent Documents 9 and 10whereby hexamethyldisilane is added for the purpose of forming a coatingon a negative electrode surface, the publications merely introduce thecompound as an example of large numbers of additives, and do notdescribe a technique related to combining these additives. Further, thepublications do not specifically test the effect of combining suchadditives.

Further, in Patent Documents 9 and 10, adding hexamethyldisilane to theelectrolytic solution is described as being effective in reducingirreversible capacity and suppressing the degradation reaction of theelectrolytic solution at the negative electrode. It is not known how theaddition of hexamethyldisilane to the electrolytic solution affects thelow-temperature discharge characteristics and/or cycle characteristics.

The present invention has been made over the foregoing backgrounds, andit is an object of the present invention to provide a nonaqueouselectrolytic solution of excellent low-temperature dischargecharacteristics and/or cycle characteristics for use in secondarybatteries, and secondary batteries using such nonaqueous electrolyticsolutions.

Means for Solving the Problems

The present inventors focused on substituents of relatively lowself-polymerizing ability, and found that the low-temperature internalresistance can be suppressed, and the low-temperature characteristics ofa battery can be improved with the use of compounds that do not haveunsaturated bond-containing aliphatic substituents but have Si—Si bonds,without increasing the degree of polymerization of the coating. Thepresent inventors also found that adding other specific compounds cangreatly improve low-temperature discharge characteristics whilemaintaining the cycle characteristics comparative to the cyclecharacteristics of conventional batteries. The present invention hasbeen completed on the basis of these findings.

Specifically, the present invention provides the following nonaqueouselectrolytic solutions.

<1>

A nonaqueous electrolytic solution for use in a nonaqueous electrolyticsolution secondary battery that comprises a negative electrode and apositive electrode capable of storing and releasing metal ions, and anonaqueous electrolytic solution,

wherein the nonaqueous electrolytic solution contains the following (A)and (B):

(A) a compound that does not have an aliphatic substituent having anunsaturated bond but has a Si—Si bond;

(B) at least one compound selected from the group consisting of acarbonate ester having an unsaturated bond, a compound represented bythe following general formula (1), a compound having a S═O group, acompound having an NCO group, monofluorophosphate, difluorophosphate,fluorosulfonate, and an imide salt,

[wherein M represents a transition metal, an element of group 13, 14, or15 of the periodic table, or a hydrocarbon group of 1 to 6 carbon atomsthat may have a heteroatom, where when M represents a transition metal,or an element of group 13, 14, or 15 of the periodic table, Z^(a+) is ametal ion, a proton, or an onium ion, a represents 1 to 3, b represents1 to 3, 1 represents b/a, m represents 1 to 4, n represents 1 to 8, trepresents 0 to 1, p represents 0 to 3, q represents 0 to 2, and rrepresents 0 to 2, and where when M is a hydrocarbon group of 1 to 6carbon atoms that may have a heteroatom, Z^(a+) does not exist, anda=b=1=n=0, m=1, t represents 0 to 1, p represents 0 to 3, q represents 0to 2, and r represents 0 to 2,

R¹ represents a halogen atom, a hydrocarbon group of 1 to 20 carbonatoms that may have a heteroatom, or X³R⁴ (where R¹ that exists innumber n may bind to one another to form a ring), R² represents a directbond, or a hydrocarbon group of 1 to 6 carbon atoms that may have aheteroatom, X¹, X², and X³ each independently represents O, S, or NR⁵,and R³, R⁴, and R⁵ each independently represent hydrogen, a hydrocarbongroup of 1 to 10 carbon atoms that may have a heteroatom (a plurality ofR³ and R⁴ may bind to one another to form a ring), and Y¹ and Y² eachindependently represent C, S, or Si, wherein, when Y¹ or Y² is C or Si,q or r is 0 or 1, and, when Y¹ or Y² is S, q and r each are 2].

<2>

The nonaqueous electrolytic solution according to the item <1> above,wherein the compound having a S═O group is a compound represented by thefollowing general formula (2),

(wherein L represents an optionally substituted organic group withvalence number α, R⁴ represents a halogen atom, a hydrocarbon group of 1to 4 carbon atoms, or an alkoxy group, a is an integer of 1 or more,and, when a is 2 or more, a plurality of R⁴ may be the same ordifferent, and wherein R⁴ and L may bind to each other to form a ring.

<3>

The nonaqueous electrolytic solution according to the item <1> above,wherein the compound having an NCO group is a compound represented bythe following general formula (3),

(wherein R⁵ represents an organic group of 1 to 20 carbon atoms that mayhave a branched structure or an aromatic group, and Q represents ahydrogen atom or an NCO group).

<4>

The nonaqueous electrolytic solution according to the item <2> or <3>above, wherein at least one compound selected from the group consistingof the carbonate ester having an unsaturated bond, the compoundrepresented by the general formula (1), the compound represented by thegeneral formula (2), and the compound represented by the general formula(3) is at least one compound selected from the group consisting ofvinylene carbonate, vinylethylene carbonate, ethynylethylene carbonate,methylpropargyl carbonate, dipropargyl carbonate, lithiumbis(oxalate)borate, lithium difluorooxalateborate, lithiumtris(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, lithiumtetrafluorooxalatephosphate, ethynylethylene sulfate, propynyl vinylsulfonate, and hexamethylene diisocyanate.

<5>

The nonaqueous electrolytic solution according to the item <1> above,wherein at least one compound selected from the group consisting of themonofluorophosphate, the difluorophosphate, the fluorosulfonate, and theimide salt is at least one compound selected from the group consistingof lithium monofluorophosphate, lithium difluorophosphate, lithiumfluorosulfonate, LiN(FSO₂)₂, LiN(CF₃SO₂)₂, and LiN(C₂F₅SO₂)₂.

<6>

A nonaqueous electrolytic solution for use in a nonaqueous electrolyticsolution secondary battery that comprises a positive electrode capableof storing and releasing metal ions, a negative electrode that containsa carbonaceous material, and a nonaqueous electrolytic solution,

wherein the nonaqueous electrolytic solution contains a compound thatdoes not have an aliphatic substituent having an unsaturated bond buthas a Si—Si bond, and a carbonate ester having a halogen atom.

<7>

The nonaqueous electrolytic solution according to the item <6>, whereinthe carbonate ester having a halogen atom is at least one compoundselected from monofluoroethylene carbonate, 4,4-difluoroethylenecarbonate, and 4,5-difluoroethylene carbonate.

<8>

The nonaqueous electrolytic solution according to any one of the items<1> to <7> above, wherein the compound that does not have an aliphaticsubstituent having an unsaturated bond but has a Si—Si bond is acompound represented by the following general formula (4).

(wherein A¹ to A⁶ may be the same or different, and represent a hydrogenatom, a halogen atom, a hydrocarbon group of 1 to 10 carbon atoms thatmay have a heteroatom, or an optionally substituted hydrogen silicidegroup of 1 to 10 silicon atoms, and wherein A¹ to A⁶ may bind to oneanother to form a ring, where none of A¹ to A⁶ is an aliphaticsubstituent having an unsaturated bond).

<9>

The nonaqueous electrolytic solution according to any one of the items<1> to <8> above, wherein the compound that does not have an aliphaticsubstituent having an unsaturated bond but has a Si—Si bond is at leastone selected from the group consisting of hexamethyldisilane,hexaethyldisilane, 1,2-diphenyltetramethyldisilane, and1,1,2,2-tetraphenyldisilane.

<10>

The nonaqueous electrolytic solution according to any one of the items<1> to <9> above, which comprises the compound that does not have analiphatic substituent having an unsaturated bond but has a Si—Si bond inan amount of 0.01 mass % or more and 10 mass % or less.

<11>

A nonaqueous electrolytic solution secondary battery that comprises acarbon-based negative electrode and a positive electrode capable ofstoring and releasing metal ions, and a nonaqueous electrolyticsolution,

wherein the nonaqueous electrolytic solution is the nonaqueouselectrolytic solution of any one of the items <1> to <10>.

Advantage of the Invention

The present invention can provide a nonaqueous electrolytic solution ofdesirable characteristics, particularly low-temperature dischargecharacteristics and/or cycle characteristics, and nonaqueouselectrolytic solution secondary batteries using such nonaqueouselectrolytic solutions.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described below in detail. Theexplanations of the constituent features of the invention describedbelow are one example (a representative example) of the embodiment ofthe invention, and the invention should not be construed as beingspecified to the content described below. Various modifications of theinvention are possible within the gist of the present invention.

As used herein, “mass %” and “weight %”, “ppm by mass” and “ppm byweight”, and “parts by mass” and “parts by weight” are synonymous toeach other. Further, the unit “ppm” used alone means “ppm by weight”.

Compounds represented by formula (X) also refer to “compounds (X)”.

<1-0. Estimated Mechanism of Advantages of the Present Invention>

The advantages of the present invention include adding a compound thatdoes not have an unsaturated bond-containing aliphatic substituent buthas a Si—Si bond to a nonaqueous electrolytic solution (a firstaddition), and adding at least one selected from the group consisting ofa carbonate ester having an unsaturated bond, a compound of thefollowing general formula (1), a compound having a S═O group, and acompound containing an NCO group (a second addition). It is believedthat these additions provide a low-temperature discharge characteristicimproving effect through the effect of the first addition suppressingthe battery internal resistance, while maintaining the stability of anegative electrode coating and the resulting improvement of cyclecharacteristics at conventional levels by the second addition, asdescribed in Examples 1-1 to 1-9 below. It was also found that thepresent invention has the advantage of improving cycle characteristicsover conventional levels, as described in Examples 1-10 and 1-11.

(M represents a transition metal, an element in group 13, 14, or 15 ofthe periodic table, or a hydrocarbon group of 1 to 6 carbon atoms thatmay have a heteroatom. When M is a transition metal or an element ingroup 13, 14, or 15 of the periodic table, Z^(a+) is a metal ion, aproton, or an onium ion, a represents 1 to 3, b represents 1 to 3, 1represents b/a, m represents 1 to 4, n represents 1 to 8, t represents 0to 1, p represents 0 to 3, q represents 0 to 2, and r represents 0 to 2.When M is a hydrocarbon group of 1 to 6 carbon atoms that may have aheteroatom, Z^(a+) does not exist, and a=b=1=n=0, m=1, t represents 0 to1, p represents 0 to 3, q represents 0 to 2, and r represents 0 to 2. R¹represents a halogen atom, a hydrocarbon group of 1 to 20 carbon atomsthat may have a heteroatom, or X³R⁴ (R¹ that exists in number n may bindto one another to form a ring), R² represents a direct bond, or ahydrocarbon group of 1 to 6 carbon atoms that may have a heteroatom, X¹,X², X³ each independently represent O, S, or NR⁵, R³, R⁴, and R⁵ eachindependently represent hydrogen, a hydrocarbon group of 1 to 10 carbonatoms that may have a heteroatom (a plurality of R³ and R⁴ may bind toone another to form a ring), and Y¹ and Y² each independently representC, S, or Si. When Y¹ or Y² is C or Si, q or r is 0 or 1, and when Y1 orY2 is S, q and r are each 2.)

In the present invention, it is believed that the use of the compoundthat does not have an unsaturated bond-containing aliphatic substituentbut has a Si—Si bond improves battery low-temperature characteristics byway of suppressing low-temperature internal resistance withoutincreasing the degree of polymerization of the coating.

Presumably, this is due to the formation of a coating by the compoundthat does not have an unsaturated bond-containing aliphatic substituentbut has a Si—Si bond, not through self-polymerization, but by a chemicalinteraction or chemical reaction with the surface functional groups ofthe carbon-based negative electrode.

Further, the present invention successfully improves the cyclecharacteristics and the low-temperature discharge characteristics at thesame time from the conventional levels with the use of a negativeelectrode containing a carbonaceous material and with the nonaqueouselectrolytic solution that contains a compound that does not have anunsaturated bond-containing aliphatic substituent but has a Si—Si bond,and a carbonate ester having a halogen atom, as described in Examples1-12 and 1-13 below.

It is speculated that this effect develops by the following mechanism.The carbonate ester having a halogen atom undergoes reaction at the edgeportions of the carbonaceous negative electrode where theintercalation/deintercalation of Li ions in and out of the negativeelectrode takes place. The decomposed product of the reactionoriginating from the carbonate ester having a halogen atom promotes areaction of the compound that does not have an unsaturatedbond-containing aliphatic substituent but has a Si—Si bond, andselectively forms a coating, originating from the compound that does nothave an unsaturated bond-containing aliphatic substituent but has aSi—Si bond, at the edge portions of the carbonaceous negative electrode.Note that it was confirmed in Reference Example 1-14 that the effectobtained by the present invention does not exhibit with a Si negativeelectrode.

Further, as described in Example 2-1 or 2-2, the present invention,adding hexafluorophosphate and the compound that does not have anunsaturated bond-containing aliphatic substituent but has a Si—Si bondto the nonaqueous electrolytic solution, and adding at least onecompound selected from the group consisting of monofluorophosphate,difluorophosphate, fluorosulfonate, and an imide salt is believed toexhibit effect that is more than a simple addition of the batteryinternal resistance suppressing effects provided by these additions, butis synergy of these effects.

The compound that does not have an unsaturated bond-containing aliphaticsubstituent but has a Si—Si bond forms a low-resistance coating on thenegative electrode, whereas at least one compound selected from thegroup consisting of monofluorophosphate, difluorophosphate,fluorosulfonate, and an imide salt has the effect of suppressing theresistance of the positive electrode. It is speculated that a part ofthe negative electrode coating provided by the first effect diffusestoward the positive electrode side, and enhances the second effectwhereby the resistance of the positive electrode is suppressed.

<1-1. Electrolyte>

The electrolyte used in the nonaqueous electrolytic solution of thepresent invention is not limited, and any known electrolyte may be usedand contained in the intended nonaqueous electrolytic solution secondarybattery. When the nonaqueous electrolytic solution of the presentinvention is used for a nonaqueous electrolytic solution secondarybattery, the electrolyte is preferably a lithium salt.

Specific examples of the electrolyte include:

inorganic lithium salts such as LiClO₄, LiAsF₆, LiPF₆, Li₂CO₃, andLiBF₄; fluorine-containing organic lithium salts such as LiCF₃SO₃,LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃,LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂, LiPF₄(CF₃SO₂)₂, LiPF₄(C₂F₅SO₂)₂, LiBF₃(CF₃),LiBF₃(C₂F₅), LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂, andLiBF₂(C₂F₅SO₂)₂;

dicarboxylic acid-containing complex lithium salts such as lithiumbis(oxalate)borate, lithium difluoro(oxalate)borate, lithiumtris(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, andlithium tetrafluoro(oxalate)phosphate; and

sodium salts or potassium salts such as KPF₆, NaPF₆, NaBF₄, andCF₃SO₃Na.

Preferred are LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, andlithium bis(oxalate)borate. Particularly preferred are LiPF₆ and LiBF₄.

The electrolyte may be used either alone, or two or more electrolytesmay be used in any combination and proportion. It is preferable to usetwo specific inorganic lithium salts, or use an inorganic lithium saltwith a fluorine-containing organic lithium salt, because it suppressesgas generation during continuous charging, or deterioration afterhigh-temperature storage.

It is particularly preferable to use LiPF₆ and LiBF₄ in combination, oruse an inorganic lithium salt such as LiPF₆ and LiBF₄ in combinationwith a fluorine-containing organic lithium salt such as LiCF₃SO₃,LiN(CF₃SO₂)₂, and LiN(C₂F₅SO₂)₂.

When using LiPF₆ and LiBF₄ in combination, LiBF₄ is typically containedin preferably 0.01 mass % to 20 mass % of the total electrolyte. LiBF₄has a low degree of dissociation, and may increase the resistance of thenonaqueous electrolytic solution when contained in excess proportions.

On the other hand, when an inorganic lithium salt such as LiPF₆ andLiBF₄ is used in combination with a fluorine-containing organic lithiumsalt such as LiCF₃SO₃, LiN(CF₃SO₂)₂, and LiN(C₂F₅SO₂)₂, the desirableproportion of the inorganic lithium salt in the total lithium salt istypically from 70 mass % to 99 mass %. Generally, thefluorine-containing organic lithium salts have larger molecular weightsthan the inorganic lithium salts. When contained in excess proportions,the resistance of the nonaqueous electrolytic solution may increase asthe proportion of the nonaqueous solvent in the total nonaqueouselectrolytic solution becomes smaller.

The lithium salt in the final composition of the nonaqueous electrolyticsolution of the present invention may have any concentration, providedthat it is not detrimental to the advantages of the present invention.The concentration of the lithium salt is typically 0.5 mol/L or more,preferably 0.6 mol/L or more, more preferably 0.8 mol/L or more, andtypically 3 mol/L or less, preferably 2 mol/L or less, more preferably1.5 mol/L or less. Excessively low concentrations may cause thenonaqueous electrolytic solution to have insufficient electricconductivity. When the concentration is in excess, the viscosityincreases and the electric conductivity lowers, with the result that theperformance of the nonaqueous electrolytic solution secondary batteryusing the nonaqueous electrolytic solution of the present invention maybe lowered.

Particularly, when the main component of the nonaqueous solvent of thenonaqueous electrolytic solution is a carbonate compound such asalkylene carbonate and dialkyl carbonate, it is preferable to use LiPF₆in combination with LiBF₄, because it suppresses the capacitydeterioration due to continuous charging, though LiPF₆ may be usedalone. When used in combination, the molar ratio of LiBF₄ with respectto LiPF₆ is typically 0.005 or more, preferably 0.01 or more,particularly preferably 0.05 or more, and typically 0.4 or less,preferably 0.2 or less. When the molar ratio is too large, the batterycharacteristics after high-temperature storage tend to lower.Conversely, when too small, it becomes difficult to obtain the effect ofsuppressing the gas generation and capacity deterioration due tocontinuous charging.

When the nonaqueous solvent of the nonaqueous electrolytic solutioncontains cyclic carboxylic acid ester compounds such as γ-butyrolactoneand γ-valerolactone in 50 volume % or more, the proportion of LiBF₄ inthe total lithium salt is preferably 50 mol % or more.

<1-2. Nonaqueous Solvent>

The nonaqueous solvent contained in the nonaqueous electrolytic solutionof the present invention is not particularly limited, as long as it doesnot have adverse effects on the battery characteristics in the productbattery. Preferably, the nonaqueous solvent is one or more solvents usedfor nonaqueous electrolytic solutions, as follows.

Examples of the nonaqueous solvent commonly used include chain andcyclic carbonates, chain and cyclic carboxylic acid esters, chain andcyclic ethers, phosphorus-containing organic solvents, andsulfur-containing organic solvents. The chain carbonates are notparticularly limited. As an example of the commonly used chaincarbonates, dialkyl carbonates are preferred, and the constituent alkylgroup contains preferably 1 to 5 carbon atoms, particularly preferably 1to 4 carbon atoms.

Specific examples include dimethyl carbonate, ethyl methyl carbonate,diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate,and di-n-propyl carbonate.

Of these, dimethyl carbonate, ethyl methyl carbonate, and diethylcarbonate are preferred from the standpoint of industrial availability,and various properties in the nonaqueous electrolytic solution secondarybattery.

The cyclic carbonates are not particularly limited. As an example of thecommonly used cyclic carbonates, cyclic carbonates with the alkylenegroup containing 2 to 6 carbon atoms, particularly 2 to 4 carbon atomsare preferred.

Specific examples include ethylene carbonate, propylene carbonate, andbutylene carbonate (2-ethylethylene carbonate, cis and trans2,3-dimethylethylene carbonate).

Of these, ethylene carbonate and propylene carbonate are preferred fromthe standpoint of various properties in the nonaqueous electrolyticsolution secondary battery.

The chain carboxylic acid esters are not particularly limited. Examplesof the commonly used chain carboxylic acid esters include methylacetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butylacetate, i-butyl acetate, t-butyl acetate, methyl propionate, ethylpropionate, n-propyl propionate, i-propyl propionate, n-butylpropionate, i-butyl propionate, and t-butyl propionate.

Of these, methyl acetate, ethyl acetate, methyl propionate, and ethylpropionate are preferred from the standpoint of industrial availability,and various properties in the nonaqueous electrolytic solution secondarybattery.

The cyclic carboxylic acid esters are not particularly limited. Examplesof the commonly used cyclic carboxylic acid esters includeγ-butyrolactone, γ-valerolactone, and δ-valerolactone.

Of these, γ-butyrolactone is preferred from the standpoint of industrialavailability, and various properties in the nonaqueous electrolyticsolution secondary battery.

The chain ethers are not particularly limited. Examples of the commonlyused chain esters include dimethoxymethane, dimethoxyethane,diethoxymethane, diethoxyethane, ethoxymethoxymethane, andethoxymethoxyethane.

Of these, dimethoxyethane and diethoxyethane are preferred from thestandpoint of industrial availability, and various properties in thenonaqueous electrolytic solution secondary battery.

The cyclic ethers are not particularly limited. Examples of the commonlyused cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, andtetrahydropyran.

The phosphorus-containing organic solvents are not particularly limited.Examples of the commonly used phosphorus-containing organic solventsinclude phosphoric acid esters such as trimethyl phosphate, triethylphosphate, and triphenyl phosphate; phosphorous acid esters such astrimethyl phosphite, triethyl phosphite, and triphenyl phosphite; andphosphine oxides such as trimethylphosphine oxide, triethylphosphineoxide, and triphenylphosphine oxide.

The sulfur-containing organic solvents are not particularly limited.Examples of the commonly used sulfur-containing organic solvents includeethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methylmethanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone,diphenyl sulfone, methylphenyl sulfone, dibutyl disulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide,N,N-dimethylmethanesulfoneamide, and N,N-diethylmethanesulfoneamide.

Of these, chain and cyclic carbonates and chain and cyclic carboxylicacid esters are preferred from the standpoint of various properties inthe nonaqueous electrolytic solution secondary battery. More preferredare ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethyl acetate, methyl propionate,ethyl propionate, and γ-butyrolactone. Further preferred are ethylenecarbonate, propylene carbonate, dimethyl carbonate, ethyl methylcarbonate, diethyl carbonate, ethyl acetate, methyl propionate, andγ-butyrolactone.

These may be used either alone or in a combination of two or more.Preferably, these are used in a combination of two or more. For example,it is preferable to use a high-dielectric-constant solvent of cycliccarbonate in combination with a low-viscosity solvent such as chaincarbonate and chain ester.

An example of the preferred combinations of the nonaqueous solvents is acombination that contains a cyclic carbonate and a chain carbonate asits main components. Particularly preferred is a combination in whichthe total of the cyclic carbonate and the chain carbonate is 80 volume %or more, preferably 85 volume % or more, more preferably 90 volume % ormore with respect to the total nonaqueous solvent, and in which thevolume of the cyclic carbonate with respect to the total of the cycliccarbonate and the chain carbonate is 5 volume % or more, preferably 10volume % or more, more preferably 15 volume % or more, and typically 50volume % or less, preferably 35 volume % or less, more preferably 30volume % or less. Using this combination of nonaqueous solvents ispreferable, because it provides a good balance between the cyclecharacteristics and the high-temperature storage characteristics(particularly, the remaining capacity and high-load discharge capacityafter high-temperature storage) of the product battery.

Specific examples of the preferred combination of cyclic carbonate andchain carbonate include a combination of ethylene carbonate and dimethylcarbonate, a combination of ethylene carbonate and diethyl carbonate, acombination of ethylene carbonate and ethyl methyl carbonate, acombination of ethylene carbonate, dimethyl carbonate, and diethylcarbonate, a combination of ethylene carbonate, dimethyl carbonate, andethyl methyl carbonate, a combination of ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate, and a combination of ethylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate.

A combination of the ethylene carbonate-chain carbonate combination withpropylene carbonate is also preferred. When propylene carbonate iscontained, the volume ratio of ethylene carbonate and propylenecarbonate is preferably 99:1 to 40:60, particularly preferably 95:5 to50:50. Further, it is preferable that the proportion of the propylenecarbonate in the total nonaqueous solvent be 0.1 volume % or more,preferably 1 volume % or more, more preferably 2 volume % or more, andtypically 10 volume % or less, preferably 8 volume % or less, morepreferably 5 volume % or less, because it can provide even more improvedcharge and discharge load characteristics while maintaining theproperties of the ethylene carbonate and chain carbonate combination.

Combinations containing asymmetrical chain carbonates are furtherpreferred. Particularly preferred are those containing ethylenecarbonate, symmetrical chain carbonate, and asymmetrical chain carbonate(such as a combination of ethylene carbonate, dimethyl carbonate, andethyl methyl carbonate, a combination of ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate, and a combination of ethylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate), or those further containing propylene carbonate, becausethese combinations provide a good balance between cycle characteristicsand charge and discharge load characteristics. Of these, combinationscontaining ethyl methyl carbonate as the asymmetrical chain carbonateare preferred, and the alkyl group forming the dialkyl carbonate haspreferably 1 to 2 carbon atoms.

Other examples of the preferred mixed solvent include those containingchain esters. Particularly preferred from the standpoint of improvingthe charge and discharge load characteristics of the battery are thosecontaining chain esters in the mixed solvent of cyclic carbonate andchain carbonate. Particularly preferred as the chain esters are ethylacetate, and methyl propionate. The volume of the chain ester in thenonaqueous solvent is typically 5% or more, preferably 8% or more, morepreferably 15% or more, and typically 50% or less, preferably 35% orless, more preferably 30% or less, further preferably 25% or less.

Other examples of the preferred nonaqueous solvent include those inwhich one organic solvent selected from the group consisting of ethylenecarbonate, propylene carbonate and butylene carbonate, andγ-butyrolactone and γ-valerolactone, or a mixed solvent containing twoor more organic solvents selected from this group are contained in aproportion of 60 volume % or more with respect to the total. Preferably,such mixed solvents have a flash point of 50° C. or more, particularlypreferably 70° C. or more. A nonaqueous electrolytic solution using suchsolvents involves less solvent evaporation and leaking even when usedunder high temperature. Generally, the balance between batterycharacteristics such as between cycle characteristics and charge anddischarge load characteristics can improve with the nonaqueous solventin which the total proportion of the ethylene carbonate andγ-butyrolactone in the nonaqueous solvent is 80 volume % or more,preferably 90 volume % or more, and the volume ratio of ethylenecarbonate and γ-butyrolactone is 5:95 to 45:55, or in which the total ofthe ethylene carbonate and propylene carbonate is 80 volume % or more,preferably 90 volume % or more, and the volume ratio of ethylenecarbonate and propylene carbonate is 30:70 to 80:20.

<1-3. Specific Si Compounds>

The “compound that does not have an unsaturated bond-containingaliphatic substituent but has a Si—Si bond” (hereinafter, also referredto as “specific Si compound”) used in the present invention may be usedeither alone or in any combination of two or more. The followingspecifically describes the “specific Si compound” of the presentinvention.

The “specific Si compound” of the present invention is not particularlylimited, as long as it is a compound that does not have an unsaturatedbond-containing aliphatic substituent but has a Si—Si bond. However,from the viewpoints of industrial availability and solubility in theelectrolytic solution, the specific Si compound is preferably a compoundrepresent by the following general formula (4).

(A¹ to A⁶ may be the same or different, and represent a hydrogen atom, ahalogen atom, a hydrocarbon group of 1 to 10 carbon atoms that may havea heteroatom, or an optionally substituted hydrogen silicide group of 1to 10 silicon atoms, A¹ to A⁶ may bind to each other to form a ring.Note that none of A¹ to A⁶ is an aliphatic substituent that has anunsaturated bond.)

A¹ to A⁶ are preferably hydrocarbon groups of 1 to 10 carbon atoms, orhydrogen atoms, particularly preferably hydrocarbon groups of 1 to 10carbon atoms. Preferred examples of the hydrocarbon group of 1 to 10carbon atoms include a methyl group, an ethyl group, an n-propyl group,and i-propyl group, and n-butyl group, an i-propyl group, a t-butylgroup, a phenyl group and a hydrogen atom. Particularly preferredexamples include a methyl group, an ethyl group, a phenyl group and ahydrogen atom.

The reason the specific compound having a Si—Si bond used in the presentinvention does not have an aliphatic substituent having an unsaturatedbond is to prevent the high-resistance coating formed by theself-polymerization of the aliphatic substituent from canceling theeffect of the “specific Si compound” suppressing the battery internalresistance.

Preferred specific examples of the “specific Si compound” includecompounds represented by the following formulae (a) to (q), of which(a), (b), (e), (g), (i) to (k), and (n) are more preferred, (a), (e),(j), (k), (n) are further preferred, and (a) hexamethyldisilane, (e)hexaethyldisilane, (j) 1,2-diphenyltetramethyldisilane, and (k)1,1,2,2-tetraphenyldisilane are most preferred.

These compounds are preferred, because they are readily available in theindustry, and can thus keep the manufacturing cost of the electrolyticsolution low. Another reason is that these specific Si compounds caneasily dissolve in the nonaqueous electrolytic solution, and can helpeffectively exhibit the effect of suppressing the battery internalresistance with the high-quality coating formed by the specific Sicompounds.

When mixing the specific Si compound of the present invention in theelectrolytic solution, the specific Si compound may be mixed in anyamount, provided that it is not detrimental to the advantages of thepresent invention. The preferred lower limit is preferably 0.01 mass %or more, more preferably 0.1 mass % or more with respect to the totalnonaqueous electrolytic solution. The preferred upper limit ispreferably 10 mass % or less, more preferably 5 mass % or less, furtherpreferably 2 mass % or less, most preferably 1 mass % or less withrespect to the total nonaqueous electrolytic solution. These ranges arepreferred, because unwanted reactions can be prevented while allowingthe specific Si compound to sufficiently exhibit its effect.

<1-4. Carbonate Ester Having Unsaturated Bond, Compound of GeneralFormula (1), Compound Having S═O Group, NCO Group-Containing Compound,Monofluorophosphate, Difluorophosphate, Fluorosulfonate, and Imide Salt>

The following specifically describes the carbonate ester having anunsaturated bond, the compound of general formula (1), the compoundhaving a S═O group, and the NCO group-containing compound (hereinafter,also referred to simply as “specific compounds”) used in the presentinvention. The following also specifically describes at least onecompound selected from the group consisting of monofluorophosphate,difluorophosphate, fluorosulfonate, and an imide salt of the presentinvention (hereinafter, also referred to as “specific salts”). Thespecific compounds and the specific salts may be used either alone or inany combination of two or more.

(1-4-1. Carbonate Ester Having Unsaturated Bond)

The molecular weight of the carbonate ester having an unsaturated bondis not particularly limited, and the carbonate ester having anunsaturated bond may have any molecular weight, as long as it is notdetrimental to the advantages of the present invention. The molecularweight of the carbonate ester having an unsaturated bond is typically 50or more, preferably 80 or more, and typically 250 or less, preferably150 or less. In these molecular weight ranges, the carbonate esterhaving an unsaturated bond can have desirable solubility for thenonaqueous electrolytic solution, and can help exhibit the foregoingeffect more desirably.

The producing process of the carbonate ester having an unsaturated bondis not particularly limited, and any known process can be chosen toproduce the carbonate ester having an unsaturated bond.

The carbonate ester having an unsaturated bond may be contained in thenonaqueous electrolytic solution of the present invention either alone,or two or more may be contained in any combination and proportion.

The amount of the carbonate ester having an unsaturated bond mixed withthe nonaqueous electrolytic solution of the present invention is notparticularly limited, and the carbonate ester having an unsaturated bondmay be mixed in any amount, as long as it is not detrimental to theadvantages of the present invention. Desirably, the carbonate esterhaving an unsaturated bond is contained in the nonaqueous electrolyticsolution of the present invention at a concentration of typically 0.01mass % or more, preferably 0.1 mass % or more, more preferably 0.3 mass% or more, and typically 70 mass % or less, preferably 50 mass % orless, more preferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove, making it possible to suppress gas generation, and preventcapacity retention from being lowered.

The carbonate ester having an unsaturated bond according to the presentinvention is not particularly limited, and any carbonate ester having anunsaturated bond may be used, as long as it is a carbonate having acarbon-carbon unsaturated bond such as a carbon-carbon double bond, anda carbon-carbon triple bond. The carbonate ester having an unsaturatedbond may have a halogen atom. The carbonate ester having an unsaturatedbond also encompasses carbonates having an aromatic ring.

Examples of the carbonate ester having an unsaturated bond includevinylene carbonate derivatives, ethylene carbonate derivativessubstituted with a substituent having an aromatic ring or acarbon-carbon unsaturated bond, phenyl carbonates, vinyl carbonates, andallyl carbonates.

Specific examples of the vinylene carbonate derivatives include vinylenecarbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate,phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, and catecholcarbonate.

Specific examples of the ethylene carbonate derivatives substituted witha substituent having an aromatic ring or a carbon-carbon unsaturatedbond include vinylethylene carbonate, 4,5-divinylethylene carbonate,phenylethylene carbonate, 4,5-diphenylethylene carbonate, andethynylethylene carbonate.

Specific examples of the phenyl carbonates include diphenyl carbonate,ethylphenyl carbonate, methylphenyl carbonate, and t-butylphenylcarbonate.

Specific examples of the vinyl carbonates include divinyl carbonate, andmethylvinyl carbonate.

Specific examples of the allyl carbonates include diallyl carbonate, andallylmethyl carbonate.

Other preferred specific examples include methylpropargyl carbonate,dipropargyl carbonate, and compounds represented by the followingformulae (B1) and (B2).

Of these carbonate esters having an unsaturated bond, preferred arevinylene carbonate derivatives, and ethylene derivatives substitutedwith a substituent having an aromatic ring or a carbon-carbonunsaturated bond. Particularly, vinylene carbonate, 4,5-diphenylvinylenecarbonate, 4,5-dimethylvinylene carbonate, vinylethylene carbonate, andethynylethylene carbonate are preferably used, because these form astable interface protective coating.

Particularly preferred among these preferred carbonate esters having anunsaturated bond are compounds represented by formulae (B3) to (B7),more particularly compounds represented by formulae (B3) and (B5).

(1-4-2. Compound of General Formula (1))

The molecular weight of the compound represented by the general formula(1) below as a specific compound is not particularly limited, and may beany molecular weight, as long as it is not detrimental to the advantagesof the present invention. The molecular weight of the compound ofgeneral formula (1) is typically 100 or more, preferably 140 or more,and typically 400 or less, preferably 350 or less. In these molecularweight ranges, the solubility of the compound of the general formula (1)in the nonaqueous electrolytic solution can improve, and it becomeseasier to obtain improved effects.

(M Represents a Transition Metal, an Element of Group 13, 14, or 15 ofthe Periodic table, or a hydrocarbon group of 1 to 6 carbon atoms thatmay have a heteroatom. When M is a transition metal or an element ofgroup 13, 14, or 15 of the periodic table, Z^(a+) is a metal ion, aproton, or an onium ion, and a represents 1 to 3, b represents 1 to 3, 1represents b/a, m represents 1 to 4, n represents 1 to 8, t represents 0to 1, p represents 0 to 3, q represents 0 to 2, and r represents 0 to 2.When M is a hydrocarbon group of 1 to 6 carbon atoms that may have aheteroatom, Z^(a+) does not exist, a=b=1=n=0, m=1, t represents 0 to 1,p represents 0 to 3, q represents 0 to 2, and r represents 0 to 2.

R¹ represents a halogen atom, a hydrocarbon group of 1 to 20 carbonatoms that may have a heteroatom, or X³R⁴ (R¹ that exists in number nmay bind to one another to form a ring), R² represents a direct bond, ora hydrocarbon group of 1 to 6 carbon atoms that may have a heteroatom,X¹, X², and X³ each independently represent O, S, or NR⁵, R³, R⁴, and R⁵each independently represent hydrogen, a hydrocarbon group of 1 to 10carbon atoms that may have a heteroatom (a plurality of R³ and R⁴ maybind to one another to form a ring), and Y¹ and Y² each independentlyrepresent C, S, or Si. When Y¹ or Y² is C or Si, q or r is 0 or 1, and,when Y1 or Y2 is S, q and r are each 2.)

The producing process of the compound of the general formula (1) is notparticularly limited, and any known process can be chosen to produce thecompound of general formula (1).

The compound of general formula (1) may be contained in the nonaqueouselectrolytic solution of the present invention either alone, or two ormore may be contained in any combination and proportion.

The amount of the compound of general formula (1) mixed with thenonaqueous electrolytic solution of the present invention is notlimited, and the compound of general formula (1) may be mixed in anyamount, as long as it is not detrimental to the advantages of thepresent invention. Desirably, the compound of general formula (1) iscontained in the nonaqueous electrolytic solution of the presentinvention at a concentration of typically 0.01 mass % or more,preferably 0.1 mass % or more, more preferably 0.2 mass % or more, andtypically 70 mass % or less, preferably 50 mass % or less, morepreferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove.

Specific preferred examples of the compound of general formula (1)include compounds represented by formulae (B8) to (B14), more preferablycompounds represented by formulae (B9), (B11), and (B13).

(1-4-3. Compound Having S═O Group)

Examples of the specific compound having a S═O group include compoundsrepresented by the following general formula (2).

(L represents an optionally substituted organic group with valencenumber α, R⁴ represents a halogen atom, a hydrocarbon group of 1 to 4carbon atoms, or an alkoxy group. α is an integer of 1 or more, and,when a is 2 or more, a plurality of R⁴ may be the same or different. R⁴and L may bind to each other to form a ring.)

The following describes sulfuric acid ester and sulfonic acid ester asspecific examples of the compounds of general formula (2).

(1-4-3-1. Sulfuric Acid Ester)

The molecular weight of the specific compound sulfuric acid ester is notparticularly limited, and may be any molecular weight, as long as it isnot detrimental to the advantages of the present invention. Themolecular weight of the sulfuric acid ester is typically 100 or more,preferably 120 or more, and typically 250 or less, preferably 180 orless. In these molecular weight ranges, the solubility of the sulfuricacid ester in the nonaqueous electrolytic solution can improve, and itbecomes easier to obtain improved effects.

The producing process of the sulfuric acid ester is not particularlylimited, and any known process may be chosen to produce the sulfuricacid ester.

The sulfuric acid ester may be contained in the nonaqueous electrolyticsolution of the present invention either alone, or two or more may becontained in any combination and proportion.

The amount of the sulfuric acid ester mixed with the nonaqueouselectrolytic solution of the present invention is not limited, and thesulfuric acid ester may be mixed in any amount, as long as it is notdetrimental to the advantages of the present invention. Desirably, thesulfuric acid ester is contained in the nonaqueous electrolytic solutionof the present invention at a concentration of typically 0.01 mass % ormore, preferably 0.1 mass % or more, more preferably 0.2 mass % or more,and typically 70 mass % or less, preferably 50 mass % or less, morepreferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove.

Specific preferred examples of the sulfuric acid ester include compoundsrepresented by formulae (B15) to (B22), more preferably compoundsrepresented by formulae (B15), (B17), (B18), and (B22).

(1-4-3-2. Sulfonic Acid Ester)

The molecular weight of the specific compound sulfonic acid ester is notparticularly limited, and may be any molecular weight, as long as it isnot detrimental to the advantages of the present invention. Themolecular weight of the sulfonic acid ester is typically 100 or more,preferably 120 or more, and typically 250 or less, preferably 150 orless. In these molecular weight ranges, the solubility of the sulfonicacid ester in the nonaqueous electrolytic solution can improve, and itbecomes easier to obtain improved effects.

The producing process of the sulfonic acid ester is not particularlylimited, and any known process may be chosen to produce the sulfonicacid ester.

The sulfonic acid ester may be contained in the nonaqueous electrolyticsolution of the present invention either alone, or two or more may becontained in any combination and proportion.

The amount of the sulfonic acid ester mixed with the nonaqueouselectrolytic solution of the present invention is not limited, and thesulfonic acid ester may be mixed in any amount, as long as it is notdetrimental to the advantages of the present invention. Desirably, thesulfonic acid ester is contained in the nonaqueous electrolytic solutionof the present invention at a concentration of typically 0.01 mass % ormore, preferably 0.1 mass % or more, more preferably 0.2 mass % or more,and typically 70 mass % or less, preferably 50 mass % or less, morepreferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove.

Specific preferred examples of the sulfonic acid ester include compoundsrepresented by formulae (B23) to (B36), more preferably compoundsrepresented by formulae (B23), (B24), (B27), (B28), and (B31) to (B36).

(1-4-3. NCO Group-Containing Compound)

Examples of the NCO group-containing compound as a specific compoundinclude compounds represented by the following general formula (3).

(R⁵ represents an organic group of 1 to 20 carbon atoms that may have abranched structure or an aromatic, and Q represents a hydrogen atom oran NCO group.)

The molecular weight of the NCO group-containing compound is notparticularly limited, and may be any molecular weight, as long as it isnot detrimental to the advantages of the present invention. Themolecular weight of the NCO group-containing compound is typically 50 ormore, preferably 70 or more, and typically 250 or less, preferably 220less. In these molecular weight ranges, the solubility of the NCOgroup-containing compound in the nonaqueous electrolytic solution canimprove, and it becomes easier to obtain improved effects.

The producing process of the NCO group-containing compound is notparticularly limited, and any known process may be chosen to produce theNCO group-containing compound.

The NCO group-containing compound may be contained in the nonaqueouselectrolytic solution of the present invention either alone, or two ormore may be contained in any combination and proportion.

The amount of the NCO group-containing compound mixed with thenonaqueous electrolytic solution of the present invention is notlimited, and the NCO group-containing compound may be mixed in anyamount, as long as it is not detrimental to the advantages of thepresent invention. Desirably, the NCO group-containing compound iscontained in the nonaqueous electrolytic solution of the presentinvention at a concentration of typically 0.01 mass % or more,preferably 0.05 mass % or more, more preferably 0.1 mass % or more, andtypically 70 mass % or less, preferably 50 mass % or less, morepreferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove.

Examples of the specific preferred NCO group-containing compound includecompounds represented by formulae (B37) to (B45), more preferablycompounds represented by (B41), (B42), (B43), and (B44) (hexamethylenediisocyanate).

Preferred among the foregoing compounds are vinylene carbonate,vinylethylene carbonate, ethynylethylene carbonate, methylpropargylcarbonate, dipropargyl carbonate, lithium bis(oxalate)borate, lithiumdifluorooxalateborate, lithium tris(oxalate)phosphate, lithiumdifluorobis(oxalate)phosphate, lithium tetrafluorooxalatephosphate,ethynylethylene sulfate, propynyl vinyl sulfonate, hexamethylenediisocyanate, particularly vinylene carbonate, ethynylethylenecarbonate, lithium bis(oxalate)borate, lithiumdifluorobis(oxalate)phosphate, and hexamethylene diisocyanate, becausethese compounds provide a relatively greater effect of improving cyclecharacteristics by formation of a coating on the negative electrode ascompared to the effect of inducing an increase of internal resistance.

(1-4-6. Carbonate Ester Having Halogen Atom)

The molecular weight of the carbonate ester having a halogen atom is notparticularly limited, and may be any molecular weight, as long as it isnot detrimental to the advantages of the present invention. Themolecular weight of the carbonate ester having a halogen atom istypically 50 or more, preferably 80 or more, and typically 250 or less,preferably 150 less. In these molecular weight ranges, the solubility ofthe carbonate ester having a halogen atom in the nonaqueous electrolyticsolution can improve, and it becomes easier to obtain improved effects.

The producing process of the carbonate ester having a halogen atom isnot particularly limited, and any known process may be chosen to producethe carbonate ester having a halogen atom.

The carbonate ester having a halogen atom may be contained in thenonaqueous electrolytic solution of the present invention either alone,or two or more may be contained in any combination and proportion.

The amount of the carbonate ester having a halogen atom mixed with thenonaqueous electrolytic solution of the present invention is notlimited, and the carbonate ester having a halogen atom may be mixed inany amount, as long as it is not detrimental to the advantages of thepresent invention. Desirably, the carbonate ester having a halogen atomis contained in the nonaqueous electrolytic solution of the presentinvention at a concentration of typically 0.01 mass % or more,preferably 0.1 mass % or more, more preferably 0.3 mass % or more, andtypically 70 mass % or less, preferably 50 mass % or less, morepreferably 40 mass % or less.

In these ranges, the effect of improving cycle characteristics candevelop more easily and sufficiently when the nonaqueous electrolyticsolution of the present invention is used in nonaqueous electrolyticsolution secondary batteries. Further, high-temperature storagecharacteristics and continuous charging characteristics also tend toimprove, particularly making it possible to suppress gas generation, andprevent capacity retention from being lowered.

The carbonate having a halogen atom (hereinafter, also referred tosimply as “halogenated carbonate”) is not particularly limited, and anyhalogenated carbonate may be used, as long as it has a halogen atom.

Specific examples of the halogen atom include a fluorine atom, achlorine atom, a bromine atom, and an iodine atom, of which a fluorineatom and a chlorine atom are preferred, and a fluorine atom isparticularly preferred. The number of halogen atoms contained in thehalogenated carbonate is not particularly limited either, as long as itis 1 or more. Typically, the number of halogen atoms is 6 or less,preferably 4 or less. When the halogenated carbonate has a plurality ofhalogen atoms, the halogen atoms may be the same or different.

Examples of the halogenated carbonate include ethylene carbonatederivatives, dimethyl carbonate derivatives, ethyl methyl carbonatederivatives, and diethyl carbonate derivatives.

Specific examples of the ethylene carbonate derivatives includemonofluoroethylene carbonate, monochloroethylene carbonate,4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate,4,4-dichloroethylene carbonate, 4,5-dichloroethylene carbonate,4-fluoro-4-methylethylene carbonate, 4-chloro-4-methylethylenecarbonate, 4,5-difluoro-4-methylethylene carbonate,4,5-dichloro-4-methylethylene carbonate, 4-fluoro-5-methylethylenecarbonate, 4-chloro-5-methylethylene carbonate,4,4-difluoro-5-methylethylene carbonate, 4,4-dichloro-5-methylethylenecarbonate, 4-(fluoromethyl)-ethylene carbonate,4-(chloromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylenecarbonate, 4-(dichloromethyl)-ethylene carbonate,4-(trifluoromethyl)-ethylene carbonate, 4-(trichloromethyl)-ethylenecarbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate,4-(chloromethyl)-4-chloroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-(chloromethyl)-5-chloroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate, 4-chloro-4,5-dimethylethylenecarbonate, 4,5-difluoro-4,5-dimethylethylene carbonate,4,5-dichloro-4,5-dimethylethylene carbonate,4,4-difluoro-5,5-dimethylethylene carbonate, and4,4-dichloro-5,5-dimethylethylene carbonate.

Specific examples of the dimethyl carbonate derivatives includefluoromethyl methyl carbonate, difluoromethyl methyl carbonate,trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate,bis(difluoro)methyl carbonate, bis(trifluoro)methyl carbonate,chloromethyl methyl carbonate, dichloromethyl methyl carbonate,trichloromethyl methyl carbonate, bis(chloromethyl)carbonate,bis(dichloro)methyl carbonate, and bis(trichloro)methyl carbonate.

Specific examples of the ethyl methyl carbonate derivatives include2-fluoroethyl methyl carbonate, ethylfluoromethyl carbonate,2,2-difluoroethyl methyl carbonate, 2-fluoroethylfluoromethyl carbonate,ethyldifluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate,2,2-difluoroethylfluoromethyl carbonate, 2-fluoroethyldifluoromethylcarbonate, ethyltrifluoromethyl carbonate, 2-chloroethylmethylcarbonate, ethylchloromethyl carbonate, 2,2-dichloroethylmethylcarbonate, 2-chloroethylchloromethyl carbonate, ethyldichloromethylcarbonate, 2,2,2-trichloroethylmethyl carbonate,2,2-dichloroethylchloromethyl carbonate, 2-chloroethyldichloromethylcarbonate, and ethyltrichloromethyl carbonate.

Specific examples of the diethyl carbonate derivatives includeethyl-(2-fluoroethyl)carbonate, ethyl-(2,2-difluoroethyl)carbonate,bis(2-fluoroethyl)carbonate, ethyl-(2,2,2-trifluoroethyl)carbonate,2,2-difluoroethyl-2′-fluoroethyl carbonate,bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl-2′-fluoroethylcarbonate, 2,2,2-trifluoroethyl-2′,2′-difluoroethyl carbonate,bis(2,2,2-trifluoroethyl)carbonate, ethyl-(2-chloroethyl)carbonate,ethyl-(2,2-dichloroethyl)carbonate, bis(2-chloroethyl)carbonate,ethyl-(2,2,2-trichloroethyl)carbonate, 2,2-dichloroethyl-2′-chloroethylcarbonate, bis(2,2-dichloroethyl)carbonate,2,2,2-trichloroethyl-2′-chloroethyl carbonate,2,2,2-trichloroethyl-2′,2′-dichloroethyl carbonate, andbis(2,2,2-trichloroethyl)carbonate.

Preferred among these halogenated carbonates are carbonates having afluorine atom, more preferably ethylene carbonate derivatives having afluorine atom. Particularly preferred are monofluoroethylene carbonate,4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate,because these compounds form LiF having an interface protectivefunction.

(1-4-7. Monofluorophosphate, Difluorophosphate, Fluorosulfonate, andImide Salt)

Examples of the monofluorophosphate include lithium monofluorophosphate,sodium monofluorophosphate, potassium monofluorophosphate, magnesiummonofluorophosphate, and calcium monofluorophosphate. Examples of thedifluorophosphate include lithium difluorophosphate, sodiumdifluorophosphate, potassium difluorophosphate, magnesiumdifluorophosphate, and calcium difluorophosphate. Examples of thefluorosulfonate include lithium fluorosulfonate, sodium fluorosulfonate,potassium fluorosulfonate, magnesium fluorosulfonate, and calciumfluorosulfonate. Examples of the imide salt include LiN(FSO₂)₂,LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, and LiN(CF₃SO₂)(C₄F₉SO₂). Preferredexamples include compounds such as lithium monofluorophosphate, lithiumdifluorophosphate, lithium fluorosulfonate, LiN(FSO₂)₂, LiN(CF₃SO₂)₂,and LiN(C₂F₅SO₂)₂, as represented below by formulae (B46) to (B51).Compounds represented by formulae (B47) to (B50) are particularlypreferred, because these compounds are highly soluble in the nonaqueouselectrolytic solution, and help exhibit the effect of the specific saltmore effectively. Further, because the salts have the lithium ions ascations, the intercalation and deintercalation reaction of the lithiumions in and out of the carbon material commonly used as the negativeelectrode can reversibly proceed in batteries such as the lithium ionsecondary battery. This is advantageous in terms of not havingparticular adverse effects on the battery.

When the specific salt of the present invention is mixed with theelectrolytic solution, the specific salt may be mixed in any amount, aslong as it is not detrimental to the advantages of the presentinvention. Typically, the specific salt is mixed in preferably 0.01 mass% or more, preferably 0.1 mass % or more, and typically 20 mass % orless, preferably 10 mass % or less with respect to the total nonaqueouselectrolytic solution. These ranges are particularly desirable, becauseunnecessary reactions can be suppressed while allowing the specific saltto sufficiently exhibit its effect.

<1-5. Additive>

The nonaqueous electrolytic solution of the present invention maycontain various additives to the extent that is not detrimental to theadvantages of the present invention. When prepared with additives, anyknown additives may be used. Additives may be used either alone, or twoor more additives may be used in any combination and proportion.

<1-5-1. Other Additives>

Additives other than the specific compound are described below. Examplesof the additives other than the specific compound include overchargepreventing agents, and auxiliary agents for improving the capacityretention characteristics and cycle characteristics afterhigh-temperature storage.

<1-5-1-1. Overcharge Preventing Agent>

Specific examples of the overcharge preventing agent include aromaticcompounds, including toluene derivatives such as toluene and xylene;unsubstituted or alkyl-substituted biphenyl derivatives such asbiphenyl, 2-methylbiphenyl, 3-methylbiphenyl, and 4-methylbiphenyl;unsubstituted or alkyl-substituted terphenyl derivatives such aso-terphenyl, m-terphenyl, and p-terphenyl; partially hydrogenatedproducts of unsubstituted or alkyl-substituted terphenyl derivatives;cycloalkylbenzene derivatives such as cyclopentylbenzene andcyclohexylbenzene; alkylbenzene derivatives having tertiary carbondirectly bonded to the benzene ring, such as cumene,1,3-diisopropylbenzene, and 1,4-diisopropylbenzene; alkylbenzenederivatives having quaternary carbon directly bonded to the benzenering, such as t-butylbenzene, t-amylbenzene, and t-hexylbenzene; andaromatic compounds having an oxygen atom, such as diphenyl ether anddibenzofuran.

These overcharge preventing agents may be used alone, or two or more maybe used in any combination. When used in any combination, thecombination may be between compounds of the same category or differentcategories presented above.

Specific examples of the combinations of compounds of differentcategories include a combination of toluene derivative and biphenylderivative; a combination of toluene derivative and terphenylderivative; a combination of toluene derivative and partiallyhydrogenated product of terphenyl derivative; a combination of toluenederivative and cycloalkylbenzene derivative; a combination of toluenederivative and alkylbenzene derivative having tertiary carbon directlybonded to the benzene ring; a combination of toluene derivative andalkylbenzene derivative having quaternary carbon directly bonded to thebenzene ring; a combination of toluene derivative and aromatic compoundhaving an oxygen atom; a combination of biphenyl derivative andterphenyl derivative; a combination of biphenyl derivative and partiallyhydrogenated product of terphenyl derivative; a combination of biphenylderivative and cycloalkylbenzene derivative; a combination of biphenylderivative and alkylbenzene derivative having tertiary carbon directlybonded to the benzene ring; a combination of biphenyl derivative andalkylbenzene derivative having quaternary carbon directly bonded to thebenzene ring; a combination of biphenyl derivative and aromatic compoundhaving an oxygen atom; a combination of terphenyl derivative andpartially hydrogenated product of terphenyl derivative; a combination ofterphenyl derivative and cycloalkylbenzene derivative; a combination ofterphenyl derivative and alkylbenzene derivative having tertiary carbondirectly bonded to the benzene ring; a combination of terphenylderivative and alkylbenzene derivative having quaternary carbon directlybonded to the benzene ring; a combination of terphenyl derivative andaromatic compound having an oxygen atom; a combination of partiallyhydrogenated product of terphenyl derivative and cycloalkylbenzenederivative; a combination of partially hydrogenated product of terphenylderivative and alkylbenzene derivative having tertiary carbon directlybonded to the benzene ring; a combination of partially hydrogenatedproduct of terphenyl derivative and alkylbenzene derivative havingquaternary carbon directly bonded to the benzene ring; a combination ofpartially hydrogenated product of terphenyl derivative and aromaticcompound having an oxygen atom; a combination of cycloalkylbenzenederivative and alkylbenzene derivative having tertiary carbon directlybonded to the benzene ring; a combination of cycloalkylbenzenederivative and alkylbenzene derivative having quaternary carbon directlybonded to the benzene ring; a combination of cycloalkylbenzenederivative and aromatic compound having an oxygen atom; a combination ofalkylbenzene derivative having tertiary carbon directly bonded to thebenzene ring and alkylbenzene derivative having quaternary carbondirectly bonded to the benzene ring; a combination of alkylbenzenederivative having tertiary carbon directly bonded to the benzene ringand aromatic compound having an oxygen atom; and a combination ofalkylbenzene derivative having quaternary carbon directly bonded to thebenzene ring and aromatic compound having an oxygen atom.

Specific examples of these combinations include a combination ofbiphenyl and o-terphenyl, a combination of biphenyl and m-terphenyl, acombination of biphenyl and partially hydrogenated product of terphenylderivative, a combination of biphenyl and cumene, a combination ofbiphenyl and cyclopentylbenzene, a combination of biphenyl andcyclohexylbenzene, a combination of biphenyl and t-butylbenzene, acombination of biphenyl and t-amylbenzene, a combination of biphenyl anddiphenyl ether, a combination of biphenyl and dibenzofuran,

a combination of o-terphenyl and partially hydrogenated product ofterphenyl derivative, a combination of o-terphenyl and cumene, acombination of o-terphenyl and cyclopentylbenzene, a combination ofo-terphenyl and cyclohexylbenzene, a combination of o-terphenyl andt-butylbenzene, a combination of o-terphenyl and t-amylbenzene, acombination of o-terphenyl and diphenyl ether, a combination ofo-terphenyl and dibenzofuran,

a combination of m-terphenyl and partially hydrogenated product ofterphenyl derivative, a combination of m-terphenyl and cumene, acombination of m-terphenyl and cyclopentylbenzene, a combination ofm-terphenyl and cyclohexylbenzene, a combination of m-terphenyl andt-butylbenzene, a combination of m-terphenyl and t-amylbenzene, acombination of m-terphenyl and diphenyl ether, a combination ofm-terphenyl and dibenzofuran,

a combination of partially hydrogenated product of terphenyl derivativeand cumene, a combination of partially hydrogenated product of terphenylderivative and cyclopentylbenzene, a combination of partiallyhydrogenated product of terphenyl derivative and cyclohexylbenzene, acombination of partially hydrogenated product of terphenyl derivativeand t-butylbenzene, a combination of partially hydrogenated product ofterphenyl derivative and t-amylbenzene, a combination of partiallyhydrogenated product of terphenyl derivative and diphenyl ether, acombination of partially hydrogenated product of terphenyl derivativeand dibenzofuran,

a combination of cumene and cyclopentylbenzene, a combination of cumeneand cyclohexylbenzene, a combination of cumene and t-butylbenzene, acombination of cumene and t-amylbenzene, a combination of cumene anddiphenyl ether, a combination of cumene and dibenzofuran, a combinationof cyclohexylbenzene and t-butylbenzene, a combination ofcyclohexylbenzene and t-amylbenzene, a combination of cyclohexylbenzeneand diphenyl ether, a combination of cyclohexylbenzene and dibenzofuran,

a combination of t-butylbenzene and t-amylbenzene, a combination oft-butylbenzene and diphenyl ether, a combination of t-butylbenzene anddibenzofuran,

a combination of t-amylbenzene and diphenyl ether, a combination oft-amylbenzene and dibenzofuran, and

a combination of diphenyl ether and dibenzofuran.

When the nonaqueous electrolytic solution of the present inventioncontains the overcharge preventing agent, the overcharge preventingagent may be contained in any concentration, as long as it is notdetrimental to the advantages of the present invention. Desirably, theovercharge preventing agent may be contained in typically 0.1 mass % ormore and 5 mass % or less with respect to the total nonaqueouselectrolytic solution.

It is preferable to contain the overcharge preventing agent in thenonaqueous electrolytic solution of the present invention to the extentthat is not detrimental to the advantages of the present invention,because it improves the safety of the nonaqueous electrolytic solutionsecondary battery in case of overcharge as might occur when the batteryis used for wrong purposes, or when the overcharge protecting circuitdoes not operate normally because of errors or other malfunctions in acharging device.

<1-5-1-2. Auxiliary Agent>

Specific examples of the auxiliary agent for improving the capacityretention characteristics and cycle characteristics afterhigh-temperature storage include anhydrides of dicarboxylic acid such assuccinic acid, maleic acid, and phthalic acid;

carbonate compounds that are not “specific carbonates”, such aserythritan carbonate, and spiro-bis-dimethylene carbonate;

sulfur-containing compounds such as ethylene sulfite, 1,3-propanesultone, 1,4-butane sultone, methyl methanesulfonate, busulfan,sulfolane, sulfolene, dimethyl sulfone, diphenyl sulfone, methylphenylsulfone, dibutyl disulfide, dicyclohexyl disulfide, tetramethylthiurammonosulfide, N,N-dimethylmethanesulfoneamide, andN,N-diethylmethanesulfoneamide;

nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; and

hydrocarbon compounds such as heptane, octane, and cycloheptane.

[2. Nonaqueous Electrolytic Solution Secondary Battery]

The nonaqueous electrolytic solution secondary battery of the presentinvention includes a negative electrode and a positive electrode capableof storing and releasing ions, and the nonaqueous electrolytic solutionof the present invention.

<2-1. Battery Configuration>

The nonaqueous electrolytic solution secondary battery of the presentinvention has the same configuration as conventionally known nonaqueouselectrolytic solution secondary batteries, except for the configurationsof the negative electrode and the nonaqueous electrolytic solution.Typically, the nonaqueous electrolytic solution secondary battery of thepresent invention is configured to include the positive electrode andthe negative electrode laminated via a porous film (separator)impregnated with the nonaqueous electrolytic solution of the presentinvention, and a casing (outer package) housing the electrodes and theseparator. As such, the nonaqueous electrolytic solution secondarybattery of the present invention is not limited to a particular shape,and may have any of a cylindrical, a rectangular, a laminated, or acoin, and a large shape.

<2-2. Nonaqueous Electrolytic Solution>

The nonaqueous electrolytic solution of the present invention is used asthe nonaqueous electrolytic solution. The nonaqueous electrolyticsolution of the present invention may be used as a mixture with othernonaqueous electrolytic solutions, provided that it does not depart fromthe gist of the present invention.

<2-3. Negative Electrode>

The negative electrode active material used for the negative electrodeis described below.

The negative electrode active material is not particularly limited, aslong as it can store and release lithium ions electrochemically.Specific examples include carbonaceous materials, alloy materials, andlithium-containing metal composite oxide materials.

<2-3-1. Carbonaceous Material>

Preferred as the carbonaceous material used as the negative electrodeactive material is one selected from:

(2-3-1-1) natural graphite,

(2-3-1-2) carbonaceous material obtained after one or more heattreatments of an artificial carbonaceous substance and an artificialgraphite substance in a temperature range of 400° C. to 3,200° C.,

(2-3-1-3) carbonaceous material forming a negative electrode activematerial layer made of carbon materials having at least two differentcrystallinities, and/or in which there is a contact interface of carbonmaterials of different crystallinities, and

(2-3-1-4) carbonaceous material forming a negative electrode activematerial layer made of carbon materials having at least two differentorientations, and/or in which there is a contact interface of carbonmaterials of different orientations.

These materials are preferable, because they provide a good balancebetween initial irreversible capacity, and high current density chargeand discharge characteristics.

The carbonaceous materials (2-3-1-1) to (2-3-1-4) may be used alone, ortwo or more may be used in any combination and proportion.

Specific examples of the artificial carbonaceous substance andartificial graphite substance (2-3-1-2) include natural graphite, coalcokes, petroleum cokes, coal pitches and petroleum pitches (or coalpitches and petroleum pitches after oxidation treatment), needle cokes,pitch cokes, and carbon materials as partially graphitized materials ofneedle cokes or pitch cokes, pyrolysis products of organic materialssuch as furnace black, acetylene black, and pitch carbon fibers,carbonizable organic materials and carbides thereof, solutionsdissolving carbonizable organic materials in low-molecular organicsolvents such as benzene, toluene, xylene, quinoline, and n-hexane, andcarbides thereof.

Specific examples of the carbonizable organic materials include coal tarpitches, ranging from soft pitches to hard pitches, coal heavy oils(such as pyrolysis liquefaction oil), direct heavy oils from atmosphericresidue and vacuum residue, crude oil, decomposed petroleum heavy oils(such as ethylene tar obtained as a by-product of the pyrolysis ofproducts such as naphtha), aromatic hydrocarbon (such as acenaphthylene,decacyclene, anthracene, and phenanthrene), nitrogen atom-containingheterocyclic compounds (such as phenazine and acridine), sulfuratom-containing heterocyclic compounds (such as thiophene andbithiophene), polyphenylene (such as biphenyl and terphenyl), polyvinylchloride, polyvinyl alcohol, polyvinyl butyral, insolubilized productsof these, organic polymers such as (nitrogen-containingpolyacnylonitrile, and polypyrrole), organic polymers (such assulfur-containing polythiophene, and polystyrene), natural polymers ofpolysaccharides (such as cellulose, lignin, mannan, polygalacturonicacid, chitosan, and saccharose), thermoplastic resins (such aspolyphenylene sulfide, and polyphenylene oxide), and heat-curable resins(such as furfuryl alcohol resin, phenol-formaldehyde resin, and imideresin).

<2-3-2. Configuration, Properties, and Preparation Method ofCarbonaceous Negative Electrode>

It is desirable that the properties of the carbonaceous material, thenegative electrode containing the carbonaceous material, the techniqueused to form the electrode, the collector, and the nonaqueouselectrolytic solution secondary battery satisfy one of the followingconditions (2-3-2-1) to (2-3-2-18), or more than one of these conditionsat the same time.

(2-3-2-1) X-Ray Parameter

The d value (interlayer distance) of the lattice plane (002 plane) ofthe carbonaceous material as determined by X-ray diffraction accordingto the Gakushin method is typically 0.335 to 0.340 nm, preferably 0.335to 0.338 nm, particularly preferably 0.335 to 0.337 nm. The crystallitesize (Lc) as determined by X-ray diffraction according to the Gakushinmethod is typically 1.0 nm or more, preferably 1.5 nm or more,particularly preferably 2 nm or more.

Preferred as an amorphous carbon coating over a graphite surface is onein which the nucleus material is the graphite with a lattice plane (002plane) d value of 0.335 to 0.338 nm as determined by X-ray diffraction,and in which a carbonaceous material having a larger d value of latticeplane (002 plane) than the nucleus material as determined X-raydiffraction is adhering to the graphite surface, wherein the nucleusmaterial, and the carbonaceous material having a larger d value oflattice plane (002 plane) than the nucleus material as determined X-raydiffraction are contained in a weight ratio of 99/1 to 80/20. In thisway, it is possible to produce a high-capacity negative electrode thatdoes not easily undergo reaction with the electrolytic solution.

(2-3-2-2) Ash Content

The ash content in the carbonaceous material is preferably 1 mass % orless, more preferably 0.5 mass % or less, particularly preferably 0.1mass % or less with respect to the total mass of the carbonaceousmaterial. The lower limit is preferably 1 ppm or more. Above these ashcontent ranges by weight, there is a case where deterioration of batteryperformance by reaction with the nonaqueous electrolytic solution at thetime of charge and discharge cannot be neglected. Below these ranges,production takes a long time and large energy, and facilities forpreventing pollution. This may raise cost.

(2-3-2-3) Volume-Based Average Particle Size

The volume-based average particle size of the carbonaceous material istypically 1 μm or more, preferably 3 μm or more, further preferably 5 μmor more, particularly preferably 7 μm or more, and typically 100 μm orless, preferably 50 μm or less, more preferably 40 μm or less, furtherpreferably 30 μm or less, particularly preferably 25 μm or less asdetermined as a volume-based average particle size (median size) byusing a laser diffraction and scattering method. A volume-based averageparticle size below these ranges may cause an increase of irreversiblecapacity, which may lead to an initial battery capacity loss. Above theforegoing ranges, the coating applied in electrode production tends tohave an uneven surface, which may have undesirable effects in batteryproduction.

The volume-based average particle size is measured by dispersing acarbon powder in a 0.2 mass % aqueous solution (about 10 mL) of thesurfactant polyoxyethylene(20) sorbitan monolaurate, using a laserdiffraction and scattering particle size analyzer (Horiba Ltd.; LA-700).The median size measured as above is defined as the volume-based averageparticle size of the carbonaceous material of the present invention.

(2-3-2-4) Raman R-Value, Raman Half-Value Width

The Raman R value of the carbonaceous material is typically 0.01 ormore, preferably 0.03 or more, further preferably 0.1 or more, andtypically 1.5 or less, preferably 1.2 or less, further preferably 1 orless, particularly preferably 0.5 or less as measured by argon ion laserRaman spectroscopy.

A Raman R value above these ranges may produce excessively high particlesurface crystallinity, leaving only a few sites for lithium entrybetween layers during charge and discharge. That is, charge acceptancemay suffer. Further, when a high-density negative electrode isfabricated by pressing after coating the collector, crystals are likelyto align in directions parallel to the electrode plate. This may lowerthe load characteristics. On the other hand, above the foregoing ranges,there are cases where the crystallinity of the particle surface lowers,and reactivity to the nonaqueous electrolytic solution increases. Thismay cause reduction of efficiency, and increase of gas generation.

The Raman half-value width of the carbonaceous material near 1,580 cm⁻¹is not particularly limited, and is typically 10 cm⁻¹ or more,preferably 15 cm⁻¹ or more, and typically 100 cm⁻¹ or less, preferably80 cm⁻¹ or less, further preferably 60 cm⁻¹ or less, particularlypreferably 40 cm⁻¹ or less.

A Raman half-value width below these ranges produce excessively highparticle surface crystallinity, leaving only a few sites for lithiumentry between layers during charge and discharge. That is, chargeacceptance may suffer. Further, when a high-density negative electrodeis fabricated by pressing after coating the collector, crystals arelikely to align in directions parallel to the electrode plate. This maylower the load characteristics. On the other hand, above the foregoingranges, there are cases where the crystallinity of the particle surfacelowers, and reactivity to the nonaqueous electrolytic solutionincreases. This may cause reduction of efficiency, and increase of gasgeneration.

Raman spectral measurement is performed with a Raman spectroscope (JASCOCorporation). Specifically, a sample is allowed to free fall into ameasurement cell and fill the cell. The cell is then rotated within aplane perpendicular to a laser beam while irradiating the sample surfacein the cell with an argon ion laser. The resulting Raman spectrum isthen measured for intensity IA of peak PA near 1,580 cm⁻¹, and intensityIB of peak PB near 1,360 cm⁻¹, and the intensity ratio R (R=IB/IA) iscalculated. The Raman R value so calculated is defined as the Raman Rvalue of the carbonaceous material of the present invention. Thehalf-value width of peak PA near 1580 cm⁻¹ of the resulting Ramanspectrum is also measured, and this is defined as the Raman half-valuewidth of the carbonaceous material of the present invention.

Raman measurement conditions are as follows.

-   -   Argon ion laser wavelength: 514.5 nm    -   Laser power on sample: 15 to 25 mW    -   Resolution: 10 to 20 cm⁻¹    -   Measurement range: 1,100 cm⁻¹ to 1,730 cm⁻¹    -   Raman R value, Raman half-value width Analysis: background        treatment    -   Smoothing treatment: Convolution by simple average 5 points        (2-3-2-5) BET Specific Surface Area

The BET specific surface area of the carbonaceous material is typically0.1 m2·g⁻¹ or more, preferably 0.7 m²·g⁻¹ or more, further preferably1.0 m²·g⁻¹ or more, particularly preferably 1.5 m²·g⁻¹ or more, andtypically 100 m²·g⁻¹ or less, preferably 25 m²·g⁻¹ or less, furtherpreferably 15 m²·g⁻¹ or less, particularly preferably 10 m²·g⁻¹ or lessas measured by using the BET method.

A BET specific surface area value below these ranges tends to haveadverse effect on lithium acceptance during charge when the carbonaceousmaterial is used as negative electrode material, and may cause thelithium to more likely to deposit on the electrode surface, possiblylowering stability. On the other hand, above these ranges, there arecases where the reactivity to the nonaqueous electrolytic solutionincreases and more gas is generated when the carbonaceous material isused as negative electrode material, making it difficult to obtain adesirable battery.

Specific surface area measurement using BET method is performed asfollows. A sample is preliminarily dried at 350° C. for 15 minutes underthe stream of nitrogen using a surface area measurement device (OhkuraRiken; fully automatic surface area measurement device), and measurementis taken by single-point nitrogen adsorption BET according to the gasflow method, using a nitrogen-helium mixed gas accurately adjusted tomake the relative pressure value of nitrogen 0.3 against atmosphericpressure. The specific surface area so determined is defined as the BETspecific surface area of the carbonaceous material of the presentinvention.

(2-3-2-6) Pore Size Distribution

The pore size distribution of the carbonaceous material is calculated bymeasuring a mercury intrusion amount. Desirably, a carbonaceous materialhaving pore sizes equivalent of 0.01 μm or more and 1 μm or less has apore size distribution of typically 0.01 cm³·g⁻¹ or more, preferably0.05 cm³·g⁻¹ or more, more preferably 0.1 cm³·g⁻¹ or more, and typically0.6 cm³·g⁻¹ or less, preferably 0.4 cm³·g⁻¹ or less, more preferably 0.3cm³·g⁻¹ or less, the pore size being measured by mercury porosimetry(mercury intrusion technique) for pores created by, for example, spacesinside the particles of the carbonaceous material, irregularities formedby steps on particle surfaces, and contact surfaces between theparticles.

Above these pore size distribution ranges, large amounts of binder maybe necessary for electrode plate formation. Below these ranges, highcurrent density charge and discharge characteristics may lower, and therelaxation effect of the electrode expansion and contraction may not beobtained at the charge and discharge.

The total pore volume determined by mercury porosimetry (mercuryintrusion technique), corresponding to pores with the diameter of 0.01μm or more and 100 μm or less is typically 0.1 cm³·g⁻¹ or more,preferably 0.25 cm³·g⁻¹ or more, further preferably 0.4 cm³·g⁻¹ or more,and typically 10 cm³·g⁻¹ or less, preferably 5 cm³·g⁻¹ or less, furtherpreferably 2 cm³·g⁻¹ or less. With a total pore volume above theseranges, large amounts of binder may be necessary for electrode plateformation. Below these ranges, the dispersing effect of a thickener or abinder may not be obtained in electrode plate formation.

Average pore size is typically 0.05 μm or more, preferably 0.1 μm ormore, further preferably 0.5 μm or more, and typically 50 μm or less,preferably 20 μm or less, further preferably 10 μm or less. With anaverage pore size above these ranges, large amounts of binder may benecessary. Below these ranges, high current density charge and dischargecharacteristics may lower.

Mercury intrusion amount measurement is performed by using a mercuryporosimeter, specifically Autopore 9520 (Micromeritics). As apretreatment, a sample (about 0.2 g) is sealed inside a powder cell, anddeaerated for 10 minutes at room temperature in a vacuum (50 μmHg orless). Then, the pressure is reduced to 4 psia (about 28 kPa) tointroduce mercury. The pressure is increased from 4 psia (about 28 kPa)to 40,000 psia (about 280 MPa) in a stepwise manner, and decreased to 25psia (about 170 kPa). Here, the pressure is increased in at least 80steps, and a mercury intrusion amount is measured in each step after a10-second equilibration time.

Pore size distribution is calculated from the mercury intrusion curveobtained as above, using Washburn's equation. Note that the mercurysurface tension (γ) is 485 dyne·cm⁻¹ (1 dyne=10 μN), and the contactangle (φ) is 140°. The pore size at 50% cumulative pore volume is usedas the average pore size.

(2-3-2-7) Circularity

The circularity of the carbonaceous material as measured as a degree ofsphericity should preferably fall in the ranges below. The circularityis defined as circularity=(the circumference of an equivalent circlehaving the same area as a particle projection shape)/(the actualcircumference of the particle projection shape), and the circularity of1 provides a theoretically true sphere.

The circularity of the particles with a carbonaceous material particlesize of 3 to 40 μm becomes more desirable as it approaches 1, and ispreferably 0.1 or more, specifically 0.5 or more, more preferably 0.8 ormore, further preferably 0.85 or more, particularly preferably 0.9 ormore.

The high current density charge and discharge characteristics improve asthe circularity increases. Below these circularity ranges, thechargeability of the negative electrode active material lowers, and theresistance between particles increases. This may lower the short-timehigh current density charge and discharge characteristics.

The circularity is measured by using a flow-type particle image analyzer(for example, FPIA manufactured by Sysmex Industrial Corporation). About0.2 g of a sample is dispersed in a 0.2 mass % aqueous solution (about50 mL) of the surfactant polyoxyethylene(20) sorbitan monolaurate, andthe dispersion is irradiated with an ultrasonic wave of 28 kHz at anoutput of 60 W for 1 minute. Subsequently, a detection range isdesignated to be 0.6 to 400 μm, and measurement is made for particleshaving a particle size of 3 to 40 μm. The resulting circularity isdefined as the circularity of the carbonaceous material of the presentinvention.

A method of improving circularity is not particularly limited, and amethod that provides a sphere by spheronization treatment is preferred,because it makes the shape of the particle space more uniform in theelectrode unit. Examples of the spheronization treatment include amethod of mechanically making the shape more spherical by impartingshear force or compressive force, and a method of mechanical or physicaltreatment in which a plurality of fine particles are granulated with abinder or by the adhesion force of the particles themselves.

(2-3-2-8) True Density

The true density of the carbonaceous material is typically 1.4 g·cm⁻³ ormore, preferably 1.6 g·cm⁻³ or more, further preferably 1.8 g·cm⁻³ ormore, particularly preferably 2.0 g·cm⁻³ or more, and typically 2.26g·cm⁻³ or less. A true density below these ranges may make the carboncrystallinity too low, and increase the initial irreversible capacity.Note that the upper limits of the foregoing ranges are the theoreticalupper limits of the true density of graphite.

The true density of the carbonaceous material is measured by using aliquid phase displacement method (pycnometer method) using butanol. Thevalue so determined is defined as the true density of the carbonaceousmaterial of the present invention.

(2-3-2-9) Tap Density

The tap density of the carbonaceous material is typically 0.1 g·cm⁻³ ormore, preferably 0.5 g·cm⁻³ or more, further preferably 0.7 g·cm⁻³ ormore, particularly preferably 0.9 g·cm⁻³ or more, and preferably 2g·cm⁻³ or less, further preferably 1.8 g·cm⁻³ or less, particularlypreferably 1.6 g·cm⁻³ or less.

A tap density below these ranges makes it difficult to increase chargedensity when the material is used as the negative electrode, and ahigh-capacity battery may not be obtained. Above these ranges, the spacebetween the particles in the electrode becomes too few, and it maybecome difficult to provide conductivity between the particles, makingit difficult to obtain desirable battery characteristics.

For tap density measurement, a sample is dropped into a 20-cm³ tappingcell through a 300-μm sieve until the sample fills to the top of thecell. The sample is then tapped 1,000 times at a stroke length of 10 mm,using a powder density measurement device (for example, Tap Denser;Seishin Enterprise Co., Ltd.). The tap density is then calculated fromthe resulting volume and the sample weight. The tap density socalculated is defined as the tap density of the carbonaceous material ofthe present invention.

(2-3-2-10) Orientation Ratio

The orientation ratio of the carbonaceous material is typically 0.005 ormore, preferably 0.01 or more, further preferably 0.015 or more, andtypically 0.67 or less. An orientation ratio below these ranges maylower the high-density charge and discharge characteristics. Note thatthe upper limits of the foregoing ranges are the theoretical upperlimits of the orientation ratio of the carbonaceous material.

The orientation ratio is measured by the X-ray diffraction of a sampleafter pressure molding. A sample (0.47 g) is charged into a moldingmachine (diameter 17 mm), and molded by being compressed at 58.8 MN-m⁻².For X-ray diffraction, the resulting product is set in a measurementsample holder in a manner that makes the sample surface in flush withthe holder surface. From the peak intensities of the (110) diffractionand the (004) diffraction of the carbon, the peak intensity ratio (110)diffraction peak intensity/(004) diffraction peak intensity iscalculated. The orientation ratio so calculated is defined as theorientation ratio of the carbonaceous material of the present invention.

X-ray diffraction measurement conditions are as follows. 2θ representsdiffraction angle.

-   -   target: Cu (Kα rays) graphite monochrometer    -   slit        -   divergence slit=0.5 degrees        -   receiving slit=0.15 mm        -   scattering slit=0.5 degrees    -   measurement range and step angle/measurement time:        -   (110) plane: 75 degrees≤2θ≤80 degrees 1 degree/60 sec        -   (004) plane: 52 degrees≤2θ≤57 degrees 1 degree/60 sec            (2-3-2-11) Aspect Ratio (Powder)

The aspect ratio of the carbonaceous material is typically 1 or more,and typically 10 or less, preferably 8 or less, further preferably 5 orless. An aspect ratio above these ranges may cause lineation, and auniform coated surface may not be obtained at electrode plate formation,lowering the high current density charge and discharge characteristics.Note that the lower limits of the foregoing ranges are the theoreticallower limits of the aspect ratio of the carbonaceous material.

Aspect ratio measurement is performed by scanning electron microscopy ofthe carbonaceous material particles. Any 50 graphite particles fixed toan end surface of a metal having a thickness of 50 microns or less areselected, and a stage to which the sample is fixed is rotated and tiltedto measure each particle for diameter A (the largest diameter of thecarbonaceous material particles) and diameter B (the smallest diameterorthogonal to diameter A) by three-dimensional observation. The meanvalue of A/B is then determined. The aspect ratio (A/B) so determined isdefined as the aspect ratio of the carbonaceous material of the presentinvention.

(2-3-2-12) Mixing of Secondary Material

Mixing of secondary materials means containing two or more carbonaceousmaterials of different properties in the negative electrode and/ornegative electrode active material. Here, “properties” refers to one ormore properties selected from the group consisting of X-ray diffractionparameter, median size, aspect ratio, BET specific surface area,orientation ratio, Raman R value, tap density, true density, poredistribution, circularity, and ash content.

Particularly preferred examples of the mixing of secondary materialsinclude asymmetric volume-based particle size distribution about themedian size, containing two or more carbonaceous materials of differentRaman R values, and different X-ray parameters.

An example of the effect of mixing secondary materials is the reductionof electrical resistance by the inclusion of carbonaceous material asconductive materials, examples of which include graphite such as naturalgraphite and artificial graphite, carbon black such as acetylene black,and amorphous carbon such as needle coke.

When mixing conductive material as secondary material, the conductivematerial may be mixed alone, or two or more conductive materials may bemixed in any combination and proportion. The mixture ratio of theconductive material to the carbonaceous material is typically 0.1 mass %or more, preferably 0.5 mass % or more, further preferably 0.6 mass % ormore, and typically 45 mass % or less, preferably 40 mass % or less. Theconductivity improving effect may not be easily obtained with a mixtureratio below these ranges. Above these ranges, the initial irreversiblecapacity may increase.

(2-3-2-13) Electrode Production

Any known method can be used for electrode production, provided that itis not detrimental to the advantages of the present invention. Forexample, the electrode can be formed by adding a binder, a solvent, andoptional materials such as a thickener, a conductive material, and afiller to the negative electrode active material, and the resultingslurry is coated over the collector, which is then pressed after beingdried.

The thickness of the negative electrode active material layer on oneside immediately before the battery nonaqueous electrolytic solutioninjection step is typically 15 μm or more, preferably 20 μm or more,further preferably 30 μm or more, and typically 150 μm or less,preferably 20 μm or less, further preferably 100 μm or less. A negativeelectrode active material thickness above these ranges may lower thehigh current density charge and discharge characteristics because of thedifficulty permeating the nonaqueous electrolytic solution to regions inthe vicinity of the collector interface. Below these ranges, the volumeratio of the collector to the negative electrode active materialincreases, and the battery capacity may decrease. The negative electrodeactive material may be prepared as a sheet electrode by roll molding, ora pellet electrode by compression molding.

(2-3-2-14) Collector

The collector holding the negative electrode active material may be anyknown collector. Examples of the negative electrode collector includemetallic materials such as copper, nickel, stainless steel, andnickel-plated steel, of which copper is particularly preferred forprocessibility and cost.

When made of metallic material, the collector may have a shape of, forexample, a metal foil, a metal column, a metal coil, a metal plate, ametallic thin film, an expended metal, a punched metal, or a metal foam.Particularly preferred are metallic thin films, more preferably copperfoils, further preferably press-rolled copper foils made by pressrolling, and electrolytic copper foils made by using the electrolysistechnique. Any one of these can be used as the collector.

When the copper foil has a thickness below 25 μm, copper alloys (such asphosphor bronze, titanium copper, Corson alloy, and Cu—Cr—Zr alloy)stronger than pure copper may be used.

The collector made of copper foils produced by press rolling canpreferably be used for small cylindrical batteries, because the copperfoil collector, with its copper crystals arranged in the press rolldirection, does not easily crack even when the negative electrode istightly or sharply rolled.

The electrolytic copper foil is obtained, for example, by dipping ametallic drum in a nonaqueous electrolytic solution dissolving copperions, and current is flown while rotating the solution to cause thecopper to deposit on the drum surface. The metal can then be detached toobtain the foil. The copper formed by electrolysis may be deposited onthe surface of the press roll copper foil. One or both surfaces of thecopper foil may be subjected to a roughening treatment or a surfacetreatment (for example, such as a chromate treatment down to a thicknessof several nanometers to about 1 micrometer, and surface preparationusing Ti and the like).

Other properties desired of the collector substrate include thefollowing.

(2-3-2-14-1) Average Surface Roughness (Ra)

The average surface roughness (Ra) of the surface forming the negativeelectrode active material thin film of the collector substrate,specified by the method described in JIS B0601-1994, is not particularlylimited, and is typically 0.05 μm or more, preferably 0.1 μm or more,further preferably 0.15 μm or more, and typically 1.5 μm or less,preferably 1.3 μm or less, further preferably 1.0 μm or less. With acollector substrate average surface roughness (Ra) in these ranges,desirable charge and discharge cycle characteristics can be expected.Further, the area of the interface with the negative electrode activematerial thin film increases, and the adhesion to the negative electrodeactive material thin film improves. The upper limit of average surfaceroughness (Ra) is not particularly limited, and is typically 1.5 μm orless, because foils with an average surface roughness (Ra) exceeding 1.5μm is not commonly available as a foil of practical thickness.

(2-3-2-14-2) Tensile Strength

Tensile strength is the quotient obtained by dividing the maximumtensile force required to fracture a test piece by the test piece crosssectional area. The tensile strength used in the present invention ismeasured by using a device and a method similar to those described inJIS Z2241 (metallic material tensile testing method).

The tensile strength of the collector substrate is not particularlylimited, and is typically 100 N·mm⁻² or more, preferably 250 N·mm⁻² ormore, further preferably 400 N·mm⁻² or more, particularly preferably 500N·mm⁻² or more. Preferably, the tensile strength should be as high aspossible; however, from the viewpoint of industrial availability, thetypical value of tensile strength is 1,000 N·mm⁻² or less. With acollector substrate having high tensile strength, cracking of thecollector substrate resulting from the expansion and contraction of thenegative electrode active material thin film due to charge and dischargecan be suppressed, and desirable cycle characteristics can be obtained.

(2-3-2-14-3) 0.2% Bearing Force

0.2% Bearing force is the magnitude of the load required to cause 0.2%plastic (permanent) distortion, and it means that 0.2% deformationremains even after the removal of the applied load of this magnitude.0.2% Bearing force is measured by using a device and a method similar tothose used for the tensile strength measurement.

The 0.2% bearing force of the collector substrate is not particularlylimited, and is typically 30 N·mm⁻² or more, preferably 150 N·mm⁻² ormore, particularly preferably 300 N·mm⁻² or more. The value of 0.2%bearing force should be as high as possible. However, it is desirablethat the 0.2% bearing force is typically 900 N·mm⁻² or less from theviewpoint of industrial availability. With a collector substrate of ahigh 0.2% bearing force, the plastic deformation of the collectorsubstrate resulting from the expansion and contraction of the negativeelectrode active material thin film due to charge and discharge can besuppressed, and desirable cycle characteristics can be obtained.

(2-3-2-14-4) Collector Thickness

The collector may have any thickness, and the collector thickness istypically 1 μm or more, preferably 3 μm or more, further preferably 5 μmor more, and typically 1 mm or less, preferably 100 μm or less, furtherpreferably 50 μm or less. A metal coating thickness less than 1 μmlowers strength, and may make the coating application difficult. Athickness above 100 μm may cause deformation in the shape of battery,such as rolling. The collector may be meshed.

(2-3-2-15) Thickness Ratio of Collector and Negative Electrode ActiveMaterial Layer

The thickness ratio of the collector and the negative electrode activematerial layer is not particularly limited, and the value of “(thethickness of the negative electrode active material layer on one sideimmediately before the nonaqueous electrolytic solutioninjection)/(collector thickness)” is preferably 150 or less, furtherpreferably 20 or less, particularly preferably 10 or less, andpreferably 0.1 or more, further preferably 0.4 or more, particularlypreferably 1 or more.

A thickness ratio of the collector and the negative electrode activematerial layer above the foregoing ranges may cause the collector togenerate heat by Joule heating during high current density charge anddischarge. Below the foregoing ranges, the volume ratio of the collectorwith respect to the negative electrode active material may increase, andthe battery capacity may be reduced.

(2-3-2-16) Electrode Density

The electrode structure of the electrode formed from the negativeelectrode active material is not particularly limited, and the densityof the negative electrode active material present on the collector ispreferably 1 g·cm⁻³ or more, further preferably 1.2 g·cm⁻³ or more,particularly preferably 1.3 g·cm⁻³ or more, and preferably 2 g·cm⁻³ orless, more preferably 1.9 g·cm⁻³ or less, further preferably 1.8 g·cm⁻³or less, particularly preferably 1.7 g·cm⁻³ or less. When the density ofthe negative electrode active material present on the collector is abovethe foregoing ranges, the negative electrode active material particlesmay be destroyed. This may lead to deterioration of high current densitycharge and discharge characteristics by the increased initialirreversible capacity, and the poor permeation of the nonaqueouselectrolytic solution in the vicinity of the collector/negativeelectrode active material interface. Below the foregoing ranges, theconductivity between the negative electrode active materials decreasesand the battery resistance increases, with the result that the capacityper unit volume may decrease.

(2-3-2-17) Binder

The binder used to bind the negative electrode active material is notparticularly limited, as long as the binder is a stable material againstthe solvent used for the production of the nonaqueous electrolyticsolution and the electrode.

Specific examples include resin polymers such as polyethylene,polypropylene, polyethylene terephthalate, polymethylmethacrylate,aromatic polyamide, cellulose, and nitrocellulose; rubber polymers suchas SBR (styrene⋅butadiene rubber), isoprene rubber, butadiene rubber,fluororubber, NBR (acrylonitrile⋅butadiene rubber), andethylene⋅propylene rubber; styrene-butadiene-styrene block copolymer andhydrogenation products thereof; thermoplastic elastomer polymers such asEPDM (ethylene⋅propylene⋅diene ternary copolymer),styrene⋅ethylene⋅butadiene⋅styrene copolymer, styrene⋅isoprene⋅styreneblock copolymer and hydrogenation products thereof; soft resin polymerssuch as syndiotactic-1,2-polybutadiene, polyvinyl acetate,ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer;fluoropolymers such as polyvinylidene fluoride, polytetrafluoroethylene,fluorinatepolyvinylidene fluoride, and polytetrafluoroethylene⋅ethylenecopolymer; and polymer compositions having alkali metal ion(particularly lithium ions) ion conductivity. These may be used alone,or two or more may be used in any combination and proportion.

The solvent used to form the slurry is not particularly limited, as longas it is a solvent capable of dissolving or dispersing the negativeelectrode active material, the binder, and the optionally used thickenerand conductive material. The solvent may be a water-based solvent or anorganic solvent.

Examples of the water-based solvent include water, and alcohol. Examplesof the organic solvent include N-methylpyrrolidone (NMP),dimethylformamide, dimethylacetoamide, methyl ethyl ketone,cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine,N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone,diethyl ether, dimethylacetoamide, hexamethylphosphoramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, andhexane.

When the water-based solvent is used, it is preferable to contain adispersant or the like with the thickener, and form the slurry with alatex such as SBR. These solvents may be used alone, or two or more maybe used in any combination and proportion.

The proportion of the binder with respect to the negative electrodeactive material is preferably 0.1 mass % or more, further preferably 0.5mass % or more, particularly preferably 0.6 mass % or more, andpreferably 20 mass % or less, more preferably 15 mass % or less, furtherpreferably 10 mass % or less, particularly preferably 8 mass % or less.When the proportion of the binder with respect to the negative electrodeactive material exceeds the foregoing ranges, the binder proportion thatdoes not contribute to battery capacity increases, and the batterycapacity may decrease. Below the foregoing ranges, the strength of thenegative electrode may decrease.

When the rubber polymer as represented by SBR is contained as a maincomponent, the proportion of the binder with respect to the negativeelectrode active material is typically 0.1 mass % or more, preferably0.5 mass % or more, further preferably 0.6 mass % or more, and typically5 mass % or less, preferably 3 mass % or less, further preferably 2 mass% or less.

When the fluoropolymer as represented by polyvinylidene fluoride iscontained as a main component, the proportion with respect to thenegative electrode active material is typically 1 mass % or more,preferably 2 mass % or more, further preferably 3 mass % or more, andtypically 15 mass % or less, preferably 10 mass % or less, furtherpreferably 8 mass % or less.

Typically, the thickener is used to adjust the viscosity of the slurry.The thickener is not particularly limited. Specific examples includecarboxymethylcellulose, methylcellulose, hydroxymethylcellulose,ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylatedstarch, casein, and salts thereof. These may be used alone, or two ormore may be used in any combination and proportion.

When using a thickener, the proportion of the thickener with respect tothe negative electrode active material is typically 0.1 mass % or more,preferably 0.5 mass % or more, further preferably 0.6 mass % or more,and typically 5 mass % or less, preferably 3 mass % or less, furtherpreferably 2 mass % or less. Ease of coating may suffer greatly when theproportion of the thickener with respect to the negative electrodeactive material is below these ranges. Above the foregoing ranges, theproportion of the negative electrode active material in the negativeelectrode active material layer decreases, which may cause the problemof low battery capacity, or may increase the resistance between thenegative electrode active materials.

(2-3-2-18) Electrode Plate Orientation Ratio

The electrode plate orientation ratio is typically 0.001 or more,preferably 0.005 or more, further preferably 0.01 or more, and typically0.67 or less. An electrode plate orientation ratio below these rangesmay lower the high-density charge and discharge characteristics. Notethat the upper limits of the foregoing ranges are the theoretical upperlimits of the electrode plate orientation ratio of the carbonaceousmaterial.

The electrode plate orientation ratio is measured by the X-raydiffraction measurement of the negative electrode active materialorientation ratio for the negative electrode pressed to the targetdensity. The specific technique is not particularly limited. In astandard method, the peaks of the carbon (110) diffraction and (004)diffraction by X-ray diffraction are fitted for peak separation usingthe asymmetrical Pearson VII profile function, and the integralintensity is calculated for each peak of the (110) diffraction and the(004) diffraction. From the resulting integral intensities, the ratiorepresented by (110) diffraction integral intensity/(004) diffractionintegral intensity is calculated. The negative electrode active materialorientation ratio of the electrode so calculated is defined as theelectrode plate orientation ratio of the carbonaceous material of thepresent invention.

X-ray diffraction measurement conditions are as follows.

2θ represents diffraction angle.

-   -   target: Cu (Kα rays) graphite monochrometer    -   slit        -   divergence slit=1 degree        -   receiving slit=0.1 mm        -   scattering slit=1 degree    -   measurement range and step angle/measurement time:        -   (110) plane: 76.5 degrees≤2θ≤78.5 degrees 0.01 degree/3 sec        -   (004) plane: 53.5 degrees≤2θ≤56.0 degrees 0.01 degree/3 sec    -   sample preparation: electrode is fixed to a glass place with a        0.1 mm-thick double-sided tape.        <2-3-3. Metallic Compound Material, and Configuration,        Properties, and Preparation Method of Negative Electrode Using        Metallic Compound Material>

The metallic compound material used as the negative electrode activematerial is not particularly limited, and may be any of a simplesubstance metal or an alloy forming a lithium alloy, and compounds suchas the oxide, carbide, nitride, silicide, sulfide, and phosphidethereof, provided that lithium can be stored and released. Examples ofsuch metallic compounds include compounds containing metals such as Ag,Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. Preferredamong the foregoing materials are simple substance metals or alloysforming a lithium alloy, more preferably materials containing group 13or 14 metal and metalloid elements (e.g., elements other than carbon),further preferably simple substance metal silicon (Si), tin (Sn), orlead (Pb) (in the following, these three elements are also referred toas “specific metallic elements”) or alloys containing these atoms, orcompounds of these metals (specific metallic elements). These may beused alone, or two or more may be used in any combination andproportion.

Examples of the negative electrode active material having at least oneatom selected from the specific metallic elements include simplesubstance metal of any one of the specific metallic elements, an alloyof two or more of the specific metallic elements, an alloy of one ormore of the specific metallic elements and one or more other metallicelements, and compounds such as compounds containing one or morespecific metallic elements, or composite compounds such as the oxide,carbide, nitride, silicide, sulfide, and phosphide of such compounds.The battery can have high capacity when these simple substance metals,alloys, and metallic compounds are used as the negative electrode activematerial.

Other examples include compounds in which composite compounds such asabove are bonded to several different elements, such as simple substancemetals, alloys, and non-metallic elements, in a complex manner. Morespecifically, for example, in the case of silicon or tin, an alloy ofthese elements and metals that do not act as the negative electrode maybe used. Further, in the case of tin for example, it is possible to usecomplex compounds containing 5 to 6 different elements in a combinationof tin, a non-silicon metal that acts as the negative electrode, a metalthat does not act as the negative electrode, and a non-metallic element.

Among these negative electrode active materials, preferred examplesinclude any one of the specific metallic elements as a simple substancemetal, an alloy of two or more of the specific metallic elements, andoxides, carbides, and nitrides of the specific metallic elements,particularly preferably silicon and/or tin as simple substance metals,alloys thereof, and oxides, carbides, and nitrides thereof from theviewpoints of capacity per unit weight, and environmental load, becausethese materials have large capacity per unit weight in the productbattery. It is also preferable to use the following compounds containingsilicon and/or tin, because these compounds, despite the inferiorcapacity per unit weight to that offered by the simple substance metalsor alloys, excel in cycle characteristics.

-   -   Silicon and/or tin oxide with the silicon- and/or tin-to-oxygen        element ratio of typically 0.5 or more, preferably 0.7 or more,        further preferably 0.9 or more, and typically 1.5 or less,        preferably 1.3 or less, further preferably 1.1 or less    -   Silicon and/or tin nitride with the silicon- and/or        tin-to-nitrogen element ratio of typically 0.5 or more,        preferably 0.7 or more, further preferably 0.9 or more, and        typically 1.5 or less, preferably 1.3 or less, further        preferably 1.1 or less    -   Silicon and/or tin carbide with the silicon- and/or        tin-to-carbon element ratio of typically 0.5 or more, preferably        0.7 or more, further preferably 0.9 or more, and typically 1.5        or less, preferably 1.3 or less, further preferably 1.1 or less

Note that the negative electrode active materials may be used alone, ortwo or more may be used in any combination and proportion.

The negative electrode in the nonaqueous electrolytic solution secondarybattery of the present invention may be produced by using any knownmethod. Specifically, the negative electrode may be produced, forexample, by using a method in which the negative electrode activematerial is roller molded into a sheet electrode after adding a binder,a conductive material, and the like, or a method that uses compressionmolding to form a pellet electrode. Typically, a method is used in whicha thin film layer (negative electrode active material layer) thatcontains the negative electrode active material is formed on a collectorfor negative electrodes (hereinafter, also referred to as “negativeelectrode collector”), using a technique such as coating, vapordeposition, sputtering, and plating. In this case, materials such as abinder, a thickener, a conductive material, and a solvent are added tothe negative electrode active material to form a slurry material, andthis is applied onto the negative electrode collector. After drying, thewhole is pressed to increase density and form the negative electrodeactive material layer on the negative electrode collector.

Examples of the negative electrode collector material include steel, acopper alloy, nickel, a nickel alloy, and stainless steel. Preferred isa copper foil from the standpoint of ease of processing into a thinfilm, and cost.

The thickness of the negative electrode collector is typically 1 μm ormore, preferably 5 μm or more, and typically 100 μm or less, preferably50 μm or less. When the negative electrode collector is too thick, thecapacity of the battery as a whole may become excessively low. When toothin, it may pose difficulties in handling.

In order to improve the bonding with the negative electrode activematerial layer formed on the surface, it is preferable that the surfaceof the negative electrode collector be subjected to a rougheningtreatment in advance. Examples of the surface roughening method includea blast treatment, press rolling using a roughening roller, mechanicalpolishing that polishes the collector surface with a wire brush or thelike equipped with, for example, an abrasive particle-bearing coatedabrasive, a grinding stone, an emery wheel, or a steel wire,electrolytic polishing, and chemical polishing.

In order to reduce the weight of the negative electrode collector andimprove the energy density of the battery per weight, a perforatednegative electrode collector, such as an expended metal or a punchedmetal may also be used. This type of negative electrode collector canfreely adjust its weight by varying the percentage of the aperture.Further, by forming the negative electrode active material layer on theboth sides of the perforated negative electrode collector, the rivetingeffect can be provided through the holes, and the negative electrodeactive material layer does not easily detach. However, when thepercentage of the aperture is too high, the contact area between thenegative electrode active material layer and the negative electrodecollector decreases, and the bonding strength may become weak.

The slurry forming the negative electrode active material layer isproduced typically by adding a binder, a thickener, and the like to thenegative electrode material. As used herein, “negative electrodematerial” refers to a material as a mixture of the negative electrodeactive material and a conductive material.

The preferred content of the negative electrode active material in thenegative electrode material is typically 70 mass % or more, particularly75 mass % or more, and typically 97 mass % or less, particularly 95 mass% or less. When the negative electrode active material content is toosmall, the capacity of the secondary battery using the negativeelectrode tends to be insufficient. When too large, the content of thebinder and the like becomes relatively smaller, and the strength of theresulting negative electrode tends to be insufficient. When using two ormore negative electrode active materials, the total amount of thenegative electrode active materials satisfies the foregoing ranges.

Examples of the conductive materials used for the negative electrodeinclude metallic materials such as copper and nickel; and carbonmaterials such as graphite and carbon black. These may be used alone, ortwo or more may be used in any combination and proportion. It ispreferable to use carbon material as the conductive material, becausethe carbon material also serves as the active material. The preferredcontent of the conductive material in the negative electrode material istypically 3 mass % or more, particularly 5 mass % or more, and typically30 mass % or less, particularly 25 mass % or less. When the conductivematerial content is too small, conductivity tends to be insufficient.When too large, the content of the negative electrode active materialand the like becomes relatively smaller, and the battery capacity andstrength tend to be insufficient. When using two or more conductivematerials, the total amount of the conductive materials satisfies theforegoing ranges.

The binder used for the negative electrode may be any binder, providedthat it is safe to the solvent and the electrolytic solution used forelectrode production. Examples include polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadienerubber-isoprene rubber, butadiene rubber, ethylene-acrylic acidcopolymer, and ethylene⋅methacrylic acid copolymer. These may be usedalone, or two or more may be used in any combination and proportion. Thepreferred binder content is typically 0.5 parts by weight or more,particularly 1 weight part or more, and typically 10 parts by weight orless, particularly 8 parts by weight or less with respect to 100 partsby weight of the negative electrode material. When the binder content istoo small, the strength of the resulting negative electrode tends to beinsufficient. When too large, the content of the negative electrodeactive material and the like becomes relatively smaller, and the batterycapacity and conductivity tend to be insufficient. When using two ormore binders, the total amount of the binders satisfies the foregoingranges.

Examples of the thickeners used for the negative electrode includecarboxymethylcellulose, methylcellulose, hydroxymethylcellulose,ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylatedstarch, and casein. These may be used alone, or two or more may be usedin any combination and proportion. The thickener is used as required.When used, the preferred thickener content in the negative electrodeactive material layer is typically 0.5 mass % or more, and 5 mass % orless.

The slurry forming the negative electrode active material layer isprepared by optionally mixing a conductive material, a binder, and athickener with the negative electrode active material, using awater-based solvent or an organic solvent as a dispersion medium. Thewater-based solvent is typically water. However, it is also possible touse non-water solvents such as alcohols (e.g., ethanol), and cyclicamides (e.g., N-methylpyrrolidone) in a proportion of about 30 mass % orless with respect to water. Typical examples of the organic solventinclude cyclic amides such as N-methylpyrrolidone, linear amides such asN,N-dimethylformamide, and N,N-dimethylacetamide, aromatic hydrocarbonssuch as anisole, toluene, and xylene, and alcohols such as butanol, andcyclohexanol. Preferred are cyclic amides such as N-methylpyrrolidone,and linear amides such as N,N-dimethylformamide, andN,N-dimethylacetamide. These may be used alone, or two or more may beused in any combination and proportion.

The viscosity of the slurry is not particularly limited, as long as itcan be applied to the collector. The viscosity may be appropriatelyadjusted to enable coating by varying, for example, the solvent amountduring the preparation of the slurry.

The negative electrode active material layer is formed upon drying andpressing the slurry applied to the negative electrode collector. Thecoating technique is not particularly limited, and known methods per semay be used. The drying technique is not particularly limited either,and known techniques such as natural drying, heat drying, and vacuumdrying may be used.

The electrode structure of the electrode formed from the negativeelectrode active material is not particularly limited, and the densityof the active material present on the collector is preferably 1 g·cm⁻³or more, further preferably 1.2 g·cm⁻³ or more, particularly preferably1.3 g·cm⁻³ or more, and preferably 2 g·cm⁻³ or less, more preferably 1.9g·cm⁻³ or less, further preferably 1.8 g·cm⁻³ or less, particularlypreferably 1.7 g·cm⁻³ or less.

When the density of the active material present on the collector isabove the foregoing ranges, the active material particles may bedestroyed. This may lead to deterioration of high current density chargeand discharge characteristics by the increased initial irreversiblecapacity, and the poor permeation of the nonaqueous electrolyticsolution in the vicinity of the collector/active material interface.Below the foregoing ranges, there are cases where the conductivitybetween the active materials decreases and the battery resistanceincreases, causing the capacity per unit volume to decrease.

<2-3-4. Lithium-Containing Metal Composite Oxide Material, andConfiguration, Properties, and Preparation Method of Negative ElectrodeUsing Lithium-Containing Metal Composite Oxide Material>

The lithium-containing metal composite oxide material used as thenegative electrode active material is not particularly limited, as longas it can store and release lithium. However, lithium-containingcomposite metal oxide materials containing titanium are preferred, andcomposite oxides of lithium and titanium (hereinafter, also referred toas “lithium-titanium composite oxides”) are particularly preferred.Specifically, it is particularly preferable to use a lithium-titaniumcomposite oxide having a spinel structure by containing it in thenonaqueous electrolytic solution secondary battery negative electrodeactive material, because this greatly reduces output resistance.

It is also preferable to use composite oxides in which the lithium andtitanium in the lithium-titanium composite oxide are substituted withother metallic elements, for example, at least one element selected fromthe group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, andNb.

Preferably, the metal oxide is a lithium-titanium composite oxiderepresented by general formula (3), and 0.7≤x≤1.5, 1.5≤y≤2.3, 0≤z≤1.6 inthe general formula (3). In this way, the structure at the time ofdoping and undoping of lithium ions can be stabilized.LixTiyMzO₄  (3)[In the general formula (3), M represents at least one element selectedfrom the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn,and Nb.]

Particularly preferred as the compositions of the general formula (3)are structures in which

(a) 1.2≤x≤1.4, 1.5≤y≤1.7, z=0

(b) 0.9≤x≤1.1, 1.9≤y≤2.1, z=0

(c) 0.7≤x≤0.9, 2.1≤y≤2.3, z=0.

This provides a desirable battery performance balance.

The particularly preferred representative compositions of the foregoingcompounds are (a) Li_(4/3)Ti_(5/3)O₄, (b) Li₁Ti₂O₄, and (c)Li_(4/5)Ti_(11/5)O₄. In structures with Z≠0, for example,Li_(4/3)Ti_(4/3)Al_(1/3)O₄ is preferable.

In addition to the foregoing requirements, the lithium-titaniumcomposite oxide as the negative electrode active material of the presentinvention satisfies preferably at least one of the properties, shapes,and other conditions described in sections (2-3-4-1) to (2-3-4-13)below, particularly preferably two or more of these conditions at thesame time.

(2-3-4-1) BET Specific Surface Area

The BET specific surface area of the lithium-titanium composite oxideused as the negative electrode active material is preferably 0.5 m²·g⁻¹or more, more preferably 0.7 m²·g⁻¹ or more, further preferably 1.0m²·g⁻¹ or more, particularly preferably 1.5 m²·g⁻¹ or more, andpreferably 200 m²·g⁻¹ or less, more preferably 100 m²·g⁻¹ or less,further preferably 50 m²·g⁻¹ or less, particularly preferably 25 m²·g⁻¹or less as measured by using the BET method.

A BET specific surface area below these ranges may decrease the reactionarea in contact with the nonaqueous electrolytic solution when thelithium-titanium composite oxide is used as the negative electrodematerial, and the output resistance may increase. Above these ranges,the crystal surfaces or the end surface portions of thetitanium-containing metal oxide may increase, causing strains in thecrystals. In this case, irreversible capacity becomes not negligible,and the desired battery may not be obtained.

Specific surface area measurement using BET method is performed asfollows. A sample is preliminarily dried at 350° C. for 15 minutes underthe stream of nitrogen using a surface area measurement device (OhkuraRiken; fully automatic surface area measurement device), and measurementis taken by single-point nitrogen adsorption BET according to the gasflow method, using a nitrogen-helium mixed gas accurately adjusted tomake the relative pressure value of nitrogen 0.3 against atmosphericpressure. The specific surface area so determined is defined as the BETspecific surface area of the lithium-titanium composite oxide of thepresent invention.

(2-3-4-2) Volume-Based Average Particle Size

The volume-based average particle size (secondary particle size when theprimary particles are aggregated and form secondary particles) of thelithium-titanium composite oxide is defined by the volume-based averageparticle size (median size) determined by using a laser diffraction andscattering method.

The volume-based average particle size of the lithium-titanium compositeoxide is typically 0.1 μm or more, preferably 0.5 μm or more, furtherpreferably 0.7 μm or more, and typically 50 μm or less, preferably 40 μmor less, further preferably μm or less, particularly preferably 25 μm orless.

The volume-based average particle size measurement is performed bydispersing a carbon powder in a 0.2 mass % aqueous solution (10 mL) ofthe surfactant polyoxyethylene(20) sorbitan monolaurate, using a laserdiffraction and scattering particle size analyzer (Horiba Ltd.; LA-700).The median size so determined is defined as the volume-based averageparticle size of the carbonaceous material of the present invention.

When the volume average particle size of the lithium-titanium compositeoxide is below the foregoing ranges, large amounts of binder will benecessary for the electrode production, and the battery capacity maydecrease as a result. Above the foregoing ranges, the coating applied inelectrode plate production tends to have an uneven surface, which mayhave undesirable effects in battery production.

(2-3-4-3) Average Primary Particle Diameter

When the primary particles aggregate and form secondary particles, theaverage primary particle diameter of the lithium-titanium compositeoxide is typically 0.01 μm or more, preferably 0.05 μm or more, furtherpreferably 0.1 μm or more, particularly preferably 0.2 μm or more, andtypically 2 μm or less, preferably 1.6 μm or less, further preferably1.3 μm or less, particularly preferably 1 μm or less. When thevolume-based average primary particle diameter is above these ranges,formation of spherical secondary particles becomes difficult. This mayhave adverse effects on powder chargeability, or greatly decrease thespecific surface area, increasing the possibility of battery performancedrop, such as in output characteristics. Below the foregoing ranges, thecrystals often become underdeveloped, and the performance of thesecondary battery may decrease, such as in reversibility of charge anddischarge.

The primary particle size is measured by scanning electron microscopy(SEM). Specifically, the value of the longest slice of the primaryparticles on the left and right of the boundary on a horizontal straightline is determined for arbitrary 50 primary particles in an image takenat a magnification (for example, 10,000 to 100,000 times) that allowsfor particle observation. The mean value of these measurements is thencalculated.

(2-3-4-4) Shape

The lithium-titanium composite oxide particles may have conventionalshapes, such as agglomerate, polyhedron, sphere, oval sphere, plate,needle, and column. Preferably, the primary particles aggregate and formsecondary particles, and the secondary particles have a spherical tooval sphere shapes.

In the electrochemical element, the active material in the electrodegenerally undergoes expansion and contraction due to charge anddischarge. The incurred stress often causes deterioration, such asdestruction of the active material, and disconnection in the conductionpath. It is therefore more preferable, in terms of relaxing the stressof expansion and contraction and preventing deterioration, that theactive material is of secondary particles formed by the aggregation ofthe primary particles, rather than simply being primary particles alone.

Further, spherical or oval sphere particles are more preferable thanparticles of equiaxial orientation such as plate-shaped particles,because the former involves less orientation in the molding of theelectrode, and less expansion and contraction of the electrode duringcharge and discharge. Spherical or oval sphere particles are alsopreferable, because these can easily be mixed in a uniform fashion withthe conductive material in electrode production.

(2-3-4-5) Tap Density

The tap density of the lithium-titanium composite oxide is preferably0.05 g·cm⁻³ or more, more preferably 0.1 g·cm⁻³ or more, furtherpreferably 0.2 g·cm⁻³ or more, particularly preferably 0.4 g·cm⁻³ ormore, and preferably 2.8 g·cm⁻³ or less, further preferably 2.4 g·cm⁻³or less, particularly preferably 2 g·cm⁻³ or less. A tap density belowthese ranges makes it difficult to increase charge density when thematerial is used as the negative electrode. Further, because of thereduced contact area between the particles, there are cases where theresistance between particles increases and causes an increase of outputresistance. Above these ranges, there are cases where the space betweenthe particles in the electrode becomes too few, and the number ofnonaqueous electrolytic solution channels decreases, with the resultthat the output resistance increase.

For tap density measurement, a sample is dropped into a 20-cm³ tappingcell through a 300-μm sieve until the sample fills to the top of thecell. The sample is then tapped 1,000 times at a stroke length of 10 mm,using a powder density measurement device (for example, Tap Denser;Seishin Enterprise Co., Ltd.). The tap density is then calculated fromthe resulting volume and the sample weight. The tap density socalculated is defined as the tap density of the lithium-titaniumcomposite oxide of the present invention.

(2-3-4-6) Circularity

The circularity of the lithium-titanium composite oxide as measured as adegree of sphericity should preferably fall in the ranges below. Thecircularity is defined as circularity=(the circumference of anequivalent circle having the same area as a particle projectionshape)/(the actual circumference of the particle projection shape), andthe circularity of 1 provides a theoretically true sphere.

The circularity of the lithium-titanium composite oxide becomes moredesirable as it approaches 1, and is typically 0.10 or more, preferably0.80 or more, further preferably 0.85 or more, particularly preferably0.90 or more. The high current density charge and dischargecharacteristics improve as the circularity increases. Thus, below thesecircularity ranges, there are cases where the chargeability of thenegative electrode active material lowers, and the resistance betweenparticles increases, lowering the short-time high current density chargeand discharge characteristics.

The circularity is measured by using a flow-type particle image analyzer(for example, FPIA manufactured by Sysmex Industrial Corporation). About0.2 g of a sample is dispersed in a 0.2 mass % aqueous solution (about50 mL) of the surfactant polyoxyethylene(20) sorbitan monolaurate, andthe dispersion is irradiated with an ultrasonic wave of 28 kHz at anoutput of 60 W for 1 minute. Subsequently, a detection range isdesignated to be 0.6 to 400 μm, and measurement is made for particleshaving a particle size of 3 to 40 μm. The resulting circularity isdefined as the circularity of the lithium-titanium composite oxide ofthe present invention.

(2-3-4-7) Aspect Ratio

The aspect ratio of the lithium-titanium composite oxide is typically 1or more, and typically 5 or less, preferably 4 or less, furtherpreferably 3 or less, particularly preferably 2 or less. An aspect ratioabove these ranges may cause lineation, and a uniform coated surface maynot be obtained at electrode plate formation, lowering the short-timehigh current density charge and discharge characteristics. Note that thelower limits of the foregoing ranges are the theoretical lower limits ofthe aspect ratio of the lithium-titanium composite oxide.

Aspect ratio measurement is performed by scanning electron microscopy ofthe lithium-titanium composite oxide particles. Any 50 particles fixedto an end surface of a metal having a thickness of 50 μm or less areselected, and a stage to which the sample is fixed is rotated and tiltedto measure each particle for diameter A (the largest diameter of theparticles) and diameter B (the smallest diameter orthogonal to diameterA) by three-dimensional observation. The mean value of A/B is thendetermined. The aspect ratio (A/B) so determined is defined as theaspect ratio of the lithium-titanium composite oxide of the presentinvention.

(2-3-4-8) Negative Electrode Active Material Producing Method

The method used to produce the lithium-titanium composite oxide is notparticularly limited, as long as it does not depart from the gist of thepresent invention. Among a number of methods available, a methodcommonly used in inorganic compound production can be used.

In an exemplary method, a titanium raw material substance such astitanium oxide is uniformly mixed with a lithium source such as LiOH,Li₂CO₃, and LiNO₃, optionally with raw material substances of otherelements. The mixture is then calcined at high temperature to obtain theactive material.

Various methods are considered available for the production of sphericalor oval-sphere active materials. In an exemplary method, a titanium rawmaterial substance such as titanium oxide, and optionally a raw materialsubstance of other element are dissolved in a solvent such as water, orpulverized and dispersed in such a solvent. The pH is adjusted whilestirring the mixture, and a spherical precursor is produced andcollected. After drying the product as required, a lithium source suchas LiOH, Li₂CO₃, and LiNO₃ is added, and the product is calcined at hightemperature to obtain the active material.

In another example, a titanium raw material substance such as titaniumoxide, and optionally a raw material substance of other element aredissolved in a solvent such as water, or pulverized and dispersed insuch a solvent. The mixture is then dry molded with a spray dryer andthe like to obtain a spherical to oval-sphere precursor. After adding alithium source such as LiOH, Li₂CO₃, and LiNO₃, the product is calcinedat high temperature to obtain the active material.

In yet another example, a titanium raw material substance such astitanium oxide, a lithium source such as LiOH, Li₂CO₃, and LiNO₃, andoptionally a raw material substance of other element are dissolved in asolvent such as water, or pulverized and dispersed in such a solvent.The mixture is then dry molded with a spray dryer and the like to obtaina spherical to oval-sphere precursor, and the product is calcined athigh temperature to obtain the active material.

In these steps, non-titanium elements, for example, such as Al, Mn, Ti,V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, C, Si, Sn, and Ag mayexist in the titanium-containing metal oxide structure, and/or incontact with the titanium-containing oxide. By containing theseelements, the activation voltage of the battery, and battery capacitycan be controlled.

(2-3-4-9) Electrode Production

Any known method can be used for electrode production. For example, theelectrode can be formed by adding a binder, a solvent, and optionalmaterials such as a thickener, a conductive material, and a filler tothe negative electrode active material, and the resulting slurry iscoated over the collector, which is then pressed after being dried.

The thickness of the negative electrode active material layer on oneside immediately before the battery nonaqueous electrolytic solutioninjection step is typically 15 μm or more, preferably 20 μm or more,more preferably 30 μm or more. The upper limit is desirably 150 μm orless, preferably 120 μm or less, more preferably 100 μm or less.

A negative electrode active material thickness above these ranges maylower the high current density charge and discharge characteristicsbecause of the difficulty permeating the nonaqueous electrolyticsolution to regions in the vicinity of the collector interface. Belowthese ranges, the volume ratio of the collector to the negativeelectrode active material may increases, and the battery capacity maydecrease. The negative electrode active material may be prepared as asheet electrode by roll molding, or a pellet electrode by compressionmolding.

(2-3-4-10) Collector

The collector holding the negative electrode active material may be anyknown collector. Examples of the negative electrode collector includemetallic materials such as copper, nickel, stainless steel, andnickel-plated steel, of which copper is particularly preferred forprocessibility and cost.

When made of metallic material, the collector may have a shape of, forexample, a metal foil, a metal column, a metal coil, a metal plate, ametallic thin film, an expended metal, a punched metal, or a metal foam.Particularly preferred are metal foil films containing copper (Cu)and/or aluminum (Al), more preferably copper foils and aluminum foils,further preferably press-rolled copper foils made by press rolling, andelectrolytic copper foils made by using the electrolysis technique. Anyone of these can be used as the collector.

When the copper foil has a thickness below 25 μm, copper alloys (such asphosphor bronze, titanium copper, Corson alloy, and Cu—Cr—Zr alloy)stronger than pure copper may be used. The aluminum foil can preferablybe used, because the aluminum foil, with its small specific gravity, canreduce the battery weight.

The collector made of copper foils produced by press rolling canpreferably be used for small cylindrical batteries, because the copperfoil collector, with its copper crystals arranged in the press rolldirection, does not easily crack even when the negative electrode istightly or sharply rolled.

The electrolytic copper foil is obtained, for example, by dipping ametallic drum in a nonaqueous electrolytic solution dissolving copperions, and current is flown while rotating the solution to cause thecopper to deposit on the drum surface. The metal can then be detached toobtain the foil. The copper formed by electrolysis may be deposited onthe surface of the press roll copper foil. One or both surfaces of thecopper foil may be subjected to a roughening treatment or a surfacetreatment (for example, such as a chromate treatment down to a thicknessof several nanometers to about 1 micrometer, and surface preparationusing Ti and the like).

Other properties desired of the collector substrate include thefollowing.

(2-3-4-10-1) Average Surface Roughness (Ra)

The average surface roughness (Ra) of the surface forming the activematerial thin film of the collector substrate, specified by the methoddescribed in JIS B0601-1994, is not particularly limited, and istypically 0.01 μm or more, preferably 0.03 μm or more, and typically 1.5μm or less, preferably 1.3 μm or less, further preferably 1.0 μm orless.

With a collector substrate average surface roughness (Ra) in theseranges, desirable charge and discharge cycle characteristics can beexpected. Further, the area of the interface with the active materialthin film increases, and the adhesion to the negative electrode activematerial thin film improves. The upper limit of average surfaceroughness (Ra) is not particularly limited, and is typically 1.5 μm orless, because foils with an average surface roughness (Ra) exceeding 1.5μm is not commonly available as a foil of practical thickness.

(2-3-4-10-2) Tensile Strength

Tensile strength is the quotient obtained by dividing the maximumtensile force required to fracture a test piece by the test piece crosssectional area. The tensile strength used in the present invention ismeasured by using a device and a method similar to those described inJIS Z2241 (metallic material tensile testing method).

The tensile strength of the collector substrate is not particularlylimited, and is typically 50 N·mm⁻² or more, preferably 100 N·mm⁻² ormore, further preferably 150 N·mm⁻² or more. Preferably, the tensilestrength should be as high as possible; however, from the viewpoint ofindustrial availability, the typical value of tensile strength isdesirably 1,000 N·mm⁻² or less.

With a collector substrate having high tensile strength, cracking of thecollector substrate resulting from the expansion and contraction of theactive material thin film due to charge and discharge can be suppressed,and desirable cycle characteristics can be obtained.

(2-3-4-10-3) 0.2% Bearing Force

0.2% Bearing force is the magnitude of the load required to cause 0.2%plastic (permanent) distortion, and it means that 0.2% deformationremains even after the removal of the applied load of this magnitude.0.2% Bearing force is measured by using a device and a method similar tothose used for the tensile strength measurement.

The 0.2% bearing force of the collector substrate is not particularlylimited, and is typically 30 N·mm⁻² or more, preferably 100 N·mm⁻² ormore, particularly preferably 150 N·mm⁻² or more. The 0.2% bearing forceshould be as high as possible. However, it is desirable that the 0.2%bearing force is typically 900 N·mm⁻² or less from the viewpoint ofindustrial availability.

With a collector substrate of a high 0.2% bearing force, the plasticdeformation of the collector substrate resulting from the expansion andcontraction of the active material thin film due to charge and dischargecan be suppressed, and desirable cycle characteristics can be obtained.

(2-3-4-10-4) Collector Thickness

The collector may have any thickness, and the collector thickness istypically 1 μm or more, preferably 3 μm or more, further preferably 5 μmor more, and typically 1 mm or less, preferably 100 μm or less, furtherpreferably 50 μm or less. A metal coating thickness less than 1 μmlowers strength, and may make the coating application difficult. Athickness above 100 μm may cause deformation in the shape of battery,such as rolling. The metallic thin film may be meshed.

(2-3-4-11) Thickness Ratio of Collector and Active Material Layer

The thickness ratio of the collector and the active material layer isnot particularly limited, and the value of “(the thickness of the activematerial layer on one side immediately before the nonaqueouselectrolytic solution injection)/(collector thickness)” is typically 150or less, preferably 20 or less, further preferably 10 or less, andtypically 0.1 or more, preferably 0.4 or more, further preferably 1 ormore.

A thickness ratio of the collector and the negative electrode activematerial layer above the foregoing ranges may cause the collector togenerate heat by Joule heating during the high current density chargeand discharge. Below the foregoing ranges, the volume ratio of thecollector with respect to the negative electrode active material mayincrease, and the battery capacity may be reduced.

(2-3-4-12) Electrode Density

The electrode structure of the electrode formed from the negativeelectrode active material is not particularly limited, and the densityof the active material present on the collector is preferably 1 g·cm⁻³or more, more preferably 1.2 g·cm⁻³ or more, further preferably 1.3g·cm⁻³ or more, particularly preferably 1.5 g·cm⁻³ or more, andpreferably 3 g·cm⁻³ or less, more preferably 2.5 g·cm⁻³ or less, furtherpreferably 2.2 g·cm⁻³ or less, particularly preferably 2 g·cm⁻³ or less.

When the density of the active material present on the collector isabove the foregoing ranges, the adhesion between the collector and thenegative electrode active material may become weak, and the electrodeand the active material may be detached from each other. Below theforegoing ranges, the conductivity between the negative electrode activematerials may decrease, and the battery resistance may increase.

(2-3-4-13) Binder

The binder used to bind the negative electrode active material is notparticularly limited, as long as the binder is a stable material againstthe solvent used for the production of the nonaqueous electrolyticsolution and the electrode.

Specific examples include resin polymers such as polyethylene,polypropylene, polyethylene terephthalate, polymethylmethacrylate,polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubberpolymers such as SBR (styrene-butadiene rubber), isoprene rubber,butadiene rubber, fluororubber, NBR (acrylonitrile⋅butadiene rubber),and ethylene⋅propylene rubber; styrene⋅butadiene⋅styrene block copolymerand hydrogenation products thereof; thermoplastic elastomer polymerssuch as EPDM (ethylene⋅propylene⋅diene ternary copolymer),styrene⋅ethylene⋅butadiene⋅styrene copolymer, styrene⋅isoprene⋅styreneblock copolymer and hydrogenation products thereof; soft resin polymerssuch as syndiotactic-1,2-polybutadiene, polyvinyl acetate,ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer;fluoropolymers such as polyvinylidene fluoride, polytetrafluoroethylene,fluorinatepolyvinylidene fluoride, and polytetrafluoroethylene⋅ethylenecopolymer; and polymer compositions having alkali metal ion(particularly lithium ions) ion conductivity. These may be used alone,or two or more may be used in any combination and proportion.

The solvent used to form the slurry is not particularly limited, as longas it is a solvent capable of dissolving or dispersing the negativeelectrode active material, the binder, and the optionally used thickenerand conductive material. The solvent may be a water-based solvent or anorganic solvent.

Examples of the water-based solvent include water, and alcohol. Examplesof the organic solvent include N-methylpyrrolidone (NMP),dimethylformamide, dimethylacetoamide, methyl ethyl ketone,cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine,N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone,dimethyl ether, dimethylacetoamide, hexamellylphosphoramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, andhexane. When the water-based solvent is used, it is preferable to add adispersant or the like with the thickener, and form the slurry with alatex such as SBR. These may be used alone, or two or more may be usedin any combination and proportion.

The proportion of the binder with respect to the negative electrodeactive material is typically 0.1 mass % or more, preferably 0.5 mass %or more, further preferably 0.6 mass % or more, and typically 20 mass %or less, preferably 15 mass % or less, further preferably 10 mass % orless, particularly preferably 8 mass % or less.

When the proportion of the binder with respect to the negative electrodeactive material exceeds the foregoing ranges, the binder proportion thatdoes not contribute to battery capacity increases, and the batterycapacity may decrease. Below the foregoing ranges, the strength of thenegative electrode may decrease, which may have undesirable effects inbattery production.

When the rubber polymer as represented by SBR is contained as a maincomponent, the proportion of the binder with respect to the activematerial is typically 0.1 mass % or more, preferably 0.5 mass % or more,further preferably 0.6 mass % or more, and typically 5 mass % or less,preferably 3 mass % or less, further preferably 2 mass % or less.

When the fluoropolymer as represented by polyvinylidene fluoride iscontained as a main component, the proportion with respect to the activematerial is 1 mass % or more, preferably 2 mass % or more, furtherpreferably 3 mass % or more, and typically 15 mass % or less, preferably10 mass % or less, further preferably 8 mass % or less.

Typically, the thickener is used to adjust the viscosity of the slurry.The thickener is not particularly limited. Specific examples includecarboxymethylcellulose, methylcellulose, hydroxymethylcellulose,ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylatedstarch, casein, and salts thereof. These may be used alone, or two ormore may be used in any combination and proportion.

When using a thickener, the proportion of the thickener with respect tothe negative electrode active material is 0.1 mass % or more, preferably0.5 mass % or more, further preferably 0.6 mass % or more, and typically5 mass % or less, preferably 3 mass % or less, further preferably 2 mass% or less. Ease of coating may suffer greatly when the proportion of thethickener with respect to the negative electrode active material isbelow these ranges. Above the foregoing ranges, the proportion of thenegative electrode active material in the active material layerdecreases, which may cause the problem of low battery capacity, or mayincrease the resistance between the negative electrode active materials.

<2-4 Positive Electrode>

The positive electrode used for the nonaqueous electrolytic solutionsecondary battery of the present invention is described below.

<2-4-1 Positive Electrode Active Material>

The following describes the positive electrode active material used forthe positive electrode.

(2-4-1-1) Composition

The positive electrode active material is not particularly limited, aslong as it can electrochemically store and release lithium ions. Apreferred example is a substance containing lithium and at least onetransition metal. Specific examples include lithium transition metalcomposite oxides, and lithium-containing transition metal phosphoricacid compounds.

Preferred examples of the transition metal of the lithium transitionmetal composite oxides include V, Ti, Cr, Mn, Fe, Co, Ni, and Cu.Specific examples include lithium-cobalt composite oxides such asLiCoO₂, lithium-nickel composite oxides such as LiNiO₂,lithium⋅manganese composite oxides such as LiMnO₂, LiMn₂O₄, and Li₂MnO₄,and lithium transition metal composite oxides in which some of the majortransition metal atoms are substituted with other metals such as Al, Ti,V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and Si.

Specific examples of such substituted lithium transition metal compositeoxides include LiNi_(0.5)Mn_(0.5)O₂, LiNi_(0.85)Co_(0.10)Al_(0.05)O₂,LiNi_(0.33)Co_(0.33)Mn_(0.33)O₂, LiMn_(1.8)Al_(0.2)O₄, andLiMn_(1.5)Ni_(0.5)O₄.

Preferred examples of the transition metal of the lithium-containingtransition metal phosphoric acid compounds include V, Ti, Cr, Mn, Fe,Co, Ni, and Cu. Specific examples include iron phosphates such asLiFePO₄, Li₃Fe₂(PO₄)₃, and LiFeP₂O₇, cobalt phosphates such as LiCoPO₄,and lithium transition metal phosphoric acid compounds in which some ofthe major transition metal atoms are substituted with other metals suchas Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

(2-4-1-2) Surface Coating

A substance of a composition different from the primary substanceforming the positive electrode active material (hereinafter, alsoreferred to as “surface adhering substance”) may be used as a coatingadhering to the surface of the positive electrode active material.Examples of the surface adhering substance include oxides such asaluminum oxide, silicon oxide, titanium oxide, zirconium oxide,magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuthoxide; sulfates such as lithium sulfate, sodium sulfate, potassiumsulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; andcarbonates such as lithium carbonate, calcium carbonate, and magnesiumcarbonate.

Various methods can be used to cause the surface adhering substance toadhere to the positive electrode active material surface, including, forexample, a method in which the surface adhering substance is dissolvedor suspended in a solvent, and dried after being added to the positiveelectrode active material through impregnation, a method in which asurface adhering substance precursor is dissolved or suspended in asolvent, and allowed to undergo reaction by means of, for example,heating after being added to the positive electrode active materialthrough impregnation, and a method in which the surface adheringsubstance is added to a positive electrode active material precursor,and calcined simultaneously.

The mass of the surface adhering substance adhering to the surface ofthe positive electrode active material is typically 0.1 ppm or more,preferably 1 ppm or more, further preferably 10 ppm or more, andtypically 20% or less, preferably 10% or less, further preferably 5% orless with respect to the mass of the positive electrode active material.

The surface adhering substance can suppress the oxidation reaction ofthe nonaqueous electrolytic solution at the positive electrode activematerial surface, and can improve battery life. The foregoing ranges arepreferable, because the surface adhering substance cannot sufficientlydevelop its effect below these ranges, and may inhibit the entry andexit of lithium ions and increase resistance above the foregoing ranges.

(2-4-1-3) Shape

The positive electrode active material particles may have conventionalshapes, such as agglomerate, polyhedron, sphere, oval sphere, plate,needle, and column. Preferably, the primary particles aggregate and formsecondary particles, and the secondary particles have a spherical or anoval sphere shape.

In the electrochemical element, the active material in the electrodegenerally undergoes expansion and contraction due to charge anddischarge. The incurred stress often causes deterioration, such asdestruction of the active material, and disconnection in the conductionpath. It is therefore more preferable, in terms of relaxing the stressof expansion and contraction and preventing deterioration, that theactive material is of secondary particles formed by the aggregation ofthe primary particles, rather than simply being primary particles alone.

Further, spherical or oval sphere particles are more preferable thanparticles of equiaxial orientation such as plate-shaped particles,because the former involves less orientation in the molding of theelectrode, and less expansion and contraction of the electrode duringcharge and discharge. Spherical or oval sphere particles are alsopreferable, because these can easily be mixed in a uniform fashion withthe conductive material in electrode production.

(2-4-1-4) Tap Density

The tap density of the positive electrode active material is typically1.3 g·cm⁻³ or more, preferably 1.5 g·cm⁻³ or more, further preferably1.6 g·cm⁻³ or more, particularly preferably 1.7 g·cm⁻³ or more, andtypically 2.5 g·cm⁻³ or less, preferably 2.4 g·cm⁻³ or less.

A high-density positive electrode active material layer can be formed byusing a metal composite oxide powder of high tap density. When the tapdensity of the positive electrode active material is below the foregoingranges, the amount of the dispersion medium needed for the positiveelectrode active material layer formation, and the required amounts ofconductive material and binder increase. This may limit the chargingrate of the positive electrode active material in the positive electrodeactive material layer, and the battery capacity. Generally, the tapdensity should be as large as possible, and the upper limit is notparticularly limited. However, below the foregoing ranges, there arecases where the diffusion of the lithium ions using the nonaqueouselectrolytic solution as a medium in the positive electrode activematerial layer becomes rate-limiting, and lowers the loadcharacteristics.

For tap density measurement, a sample is dropped into a 20-cm³ tappingcell through a 300-μm sieve until the sample fills to the cell volume.The sample is then tapped 1,000 times at a stroke length of 10 mm, usinga powder density measurement device (for example, Tap Denser; SeishinEnterprise Co., Ltd.). The tap density is then calculated from theresulting volume and the sample weight. The tap density so calculated isdefined as the tap density of the positive electrode active material ofthe present invention.

(2-4-1-5) Median Size d50

The median size d50 of the positive electrode active material particles(secondary particle size when the primary particles aggregate and formsecondary particles) may also be measured by using a laserdiffraction/scattering particle size distribution measurement device.

The median size d50 is typically 0.1 μm or more, preferably 0.5 μm ormore, further preferably 1 μm or more, particularly preferably 3 μm ormore, and typically 20 μm or less, preferably 18 μm or less, furtherpreferably 16 μm or less, particularly preferably 15 μm or less. With amedian size d50 below these ranges, a high bulk density product may notbe obtained. Above the foregoing ranges, diffusion of lithium in theparticles takes time, which may lower battery characteristics, or maycause lineation during the battery positive electrode production,specifically in forming a slurry of the active material with aconductive material, a binder, and the like, and applying the slurry inthe form of a thin film.

Chargeability in the positive electrode production can further improvewhen two or more positive electrode active materials of different mediansizes d50 are mixed in any proportion.

For median size d50 measurement, a 0.1 mass % sodium hexametaphosphateaqueous solution is used as a dispersion medium, and measurement is madeat a measurement refractive index of 1.24 after 5 minutes of ultrasonicdispersion, using a particle size analyzer (LA-920; Horiba Ltd.).

(2-4-1-6) Average Primary Particle Diameter

When the primary particles aggregate and form secondary particles, theaverage primary particle diameter of the positive electrode activematerial is typically 0.01 μm or more, preferably 0.05 μm or more, morepreferably 0.08 μm or more, particularly preferably 0.1 μm or more, andtypically 3 μm or less, preferably 2 μm or less, more preferably 1 μm orless, particularly preferably 0.6 μm or less. When the average primaryparticle diameter is above these ranges, formation of sphericalsecondary particles becomes difficult. This may have adverse effects onpowder chargeability, or may greatly decrease the specific surface area,increasing the possibility of battery performance drop, such as inoutput characteristics. Below the foregoing ranges, the crystals oftenbecome underdeveloped, and the performance of the secondary battery maydecrease, such as in reversibility of charge and discharge.

The average primary particle diameter is measured by scanning electronmicroscopy (SEM). Specifically, the value of the longest slice of theprimary particles on the left and right of the boundary on a horizontalstraight line is determined for arbitrary 50 primary particles in animage taken at a 10,000 times magnification. The mean value of thesemeasurements is then calculated.

(2-4-1-7) BET Specific Surface Area

The BET specific surface area of the positive electrode active materialis typically 0.2 m²·g⁻¹ or more, preferably 0.3 m²·g⁻¹ or more, furtherpreferably 0.4 m²·g⁻¹ or more, and typically 4.0 m²·g⁻¹ or less,preferably 2.5 m²·g⁻¹ or less, further preferably 1.5 m²·g⁻¹ or less asmeasured by using the BET method. A BET specific surface area belowthese ranges tends to lower battery performance. Above the foregoingranges, it may become difficult to increase tap density, and ease ofcoating may suffer in the positive electrode active material formation.

BET specific surface area is measured by using a surface areameasurement device (Ohkura Riken; fully automatic surface areameasurement device). A sample is preliminarily dried at 150° C. for 30minutes under the stream of nitrogen, and measurement is taken bysingle-point nitrogen adsorption BET according to the gas flow method,using a nitrogen-helium mixed gas accurately adjusted to make therelative pressure value of nitrogen 0.3 against atmospheric pressure.The specific surface area so determined is defined as the BET specificsurface area of the positive electrode active material of the presentinvention.

(2-4-1-8) Positive Electrode Active Material Producing Method

The method used to produce the positive electrode active material is notparticularly limited, as long as it does not depart from the gist of thepresent invention. Among a number of methods available, a methodcommonly used in inorganic compound production can be used.

Various methods are considered available for the production of sphericalto oval-sphere active materials. In an exemplary method, a transitionmetal raw material substance such as transition metal nitrate, andsulfate, and optionally a raw material substance of other element aredissolved in a solvent such as water, or pulverized and dispersed insuch a solvent. The pH is adjusted while stirring the mixture, and aspherical precursor is produced and collected. After drying the productas required, a lithium source such as LiOH, Li₂CO₃, and LiNO₃ is added,and the product is calcined at high temperature to obtain the activematerial.

In another example, a transition metal raw material substance such astransition metal nitrate, sulfate, hydroxide, and oxide, and optionallya raw material substance of other element are dissolved in a solventsuch as water, or pulverized and dispersed in such a solvent. Themixture is then dry molded with a spray dryer and the like to obtain aspherical to oval-sphere precursor. After adding a lithium source suchas LiOH, Li₂CO₃, and LiNO₃, the product is calcined at high temperatureto obtain the active material.

In yet another example, a transition metal raw material substance suchas transition metal nitrate, sulfate, hydroxide, and oxide, a lithiumsource such as LiOH, Li₂CO₃, and LiNO₃, and optionally a raw materialsubstance of other element are dissolved in a solvent such as water, orpulverized and dispersed in such a solvent. The mixture is then drymolded with a spray dryer and the like to obtain a spherical tooval-sphere precursor, and the product is calcined at high temperatureto obtain the active material.

<2-4-2 Electrode Structure and Electrode Producing Method>

The configuration of the positive electrode and the method of productionthereof used in the present invention are described below.

(2-4-2-1) Positive Electrode Producing Method

The positive electrode is produced by forming a positive electrodeactive material particle- and binder-containing positive electrodeactive material layer on the collector. Any known method can be used toproduce the positive electrode that uses the positive electrode activematerial. As specific examples of producing the positive electrode, thepositive electrode active material, a binder, and optional materialssuch as a conductive material and a thickener are dry mixed into a formof a sheet, and press bonded to the positive electrode collector, or aslurry prepared by dissolving or dispersing these materials in a liquidmedium is applied to the positive electrode collector, and dried to formthe positive electrode active material layer on the collector.

The content of the positive electrode active material in the positiveelectrode active material layer is typically 10 mass % or more,preferably 30 mass % or more, particularly preferably 50 mass % or more,and typically 99.9 mass % or less, preferably 99 mass % or less. Whenthe positive electrode active material content in the positive electrodeactive material layer is below these ranges, the electrical capacitancemay become insufficient. Above these ranges, the strength of thepositive electrode may become insufficient. In the present invention,the positive electrode active material powder may be used alone, or twoor more positive electrode active material powders of differentcompositions or different powder properties may be used in anycombination and proportion.

(2-4-2-2) Conductive Material

The conductive material may be any known conductive material. Specificexamples include metallic materials such as copper and nickel; graphitessuch as natural graphite, and artificial graphite; carbon black such asacetylene black; and carbonaceous materials such as amorphous carbon ofneedle coke. These may be used alone, or two or more may be used in anycombination and proportion.

The conductive material is used by being contained in the positiveelectrode active material layer in typically 0.01 mass % or more,preferably 0.1 mass % or more, more preferably 1 mass % or more, andtypically 50 mass % or less, preferably 30 mass % or less, morepreferably 15 mass % or less. When the content is below these ranges,the conductivity may become insufficient. Above these ranges, thebattery capacity may suffer.

(2-4-2-3) Binder

The binder used for the production of the positive electrode activematerial layer is not particularly limited, as long as the binder is astable material against the solvent used in the production of thenonaqueous electrolytic solution and the electrode.

In the case of coating, the binder may be a material that can bedissolved or dispersed in the liquid medium used for electrodeproduction. Specific examples include resin polymers such aspolyethylene, polypropylene, polyethylene terephthalate,polymethylmethacrylate, aromatic polyamide, cellulose, andnitrocellulose; rubber polymers such as SBR (styrene-butadiene rubber),NBR (acrylonitrile⋅butadiene rubber), fluororubber, isoprene rubber,butadiene rubber, and ethylene⋅propylene rubber; thermoplastic elastomerpolymers such as styrene-butadiene-styrene block copolymer andhydrogenation products thereof, EPDM (ethylene⋅propylene⋅diene ternarycopolymers), styrene⋅ethylene⋅butadiene⋅ethylene copolymer,styrene⋅isoprene⋅styrene block copolymer and hydrogenation productsthereof; soft resin polymers such as syndiotactic-1,2-polybutadiene,polyvinyl acetate, ethylene-vinyl acetate copolymer, andpropylene⋅α-olefin copolymer; fluoropolymers such as polyvinylidenefluoride (PVdF), polytetrafluoroethylene, fluorinatepolyvinylidenefluoride, and polytetrafluoroethylene⋅ethylene copolymer; and polymercompositions having alkali metal ion (particularly lithium ions) ionconductivity. These may be used alone, or two or more may be used in anycombination and proportion.

The proportion of the binder in the positive electrode active materiallayer is typically 0.1 mass % or more, preferably 1 mass % or more,further preferably 3 mass % or more, and typically 80 mass % or less,preferably 60 mass % or less, further preferably 40 mass % or less,particularly preferably 10 mass % or less. When the binder proportion isbelow these ranges, there are cases where the positive electrode activematerial cannot be held sufficiently, and the mechanical strength of thepositive electrode decreases, with the result that battery performancesuch as cycle characteristics lowers. Above these ranges, batterycapacity or conductivity may decrease.

(2-4-2-4) Liquid Medium

The liquid medium used to form the slurry is not particularly limited,as long as it is a solvent capable of dissolving or dispersing thepositive electrode active material, the conductive material, the binder,and the optionally used thickener. The liquid medium may be awater-based solvent or an organic solvent.

Examples of the water-based medium include water, and a mixed medium ofalcohol and water. Examples of the organic medium include hydrocarbonssuch as hexane; aromatic hydrocarbons such as benzene, toluene, xylene,and methylnaphthalene; heterocyclic compounds such as quinoline, andpyridine; ketones such as acetone, methyl ethyl ketone, andcyclohexanone; esters such as methyl acetate, and methyl acrylate;amines such as diethylenetriamine, and N,N-dimethylaminopropylamine;ethers such as diethyl ether, and tetrahydrofuran (THF); amides such asN-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetoamide;and aprotic polar solvents such as hexamethylphosphoramide, and dimethylsulfoxide. These may be used alone, or two or more may be used in anycombination and proportion.

(2-4-2-5) Thickener

When water-based medium is used as the liquid medium for forming theslurry, it is preferable to form the slurry with a thickener and a latexsuch as styrene-butadiene rubber (SBR). Typically, the thickener is usedto adjust the viscosity of the slurry.

The thickener is not limited, as long as it is not detrimental to theadvantages of the present invention. Specific examples includecarboxymethylcellulose, methylcellulose, hydroxymethylcellulose,ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylatedstarch, casein, and salts thereof. These may be used alone, or two ormore may be used in any combination and proportion.

When using a thickener, the proportion of the thickener with respect tothe active material is typically 0.1 mass % or more, preferably 0.5 mass% or more, more preferably 0.6 mass % or more, and typically 5 mass % orless, preferably 3 mass % or less, more preferably 2 mass % or less.Below these ranges, ease of coating may suffer greatly. Above theseranges, the proportion of the active material in the positive electrodeactive material layer decreases, which may cause the problem of lowbattery capacity, or may increase the resistance between the positiveelectrode active materials.

(2-4-2-6) Compaction

Preferably, the positive electrode active material layer obtained aftercoating and drying is compacted by methods such as hand pressing androller pressing to increase the charge density of the positive electrodeactive material. The density of the positive electrode active materiallayer is preferably 1 g·cm⁻³ or more, further preferably 1.5 g·cm⁻³ ormore, particularly preferably 2 g·cm⁻³ or more, and preferably 4 g·cm⁻³or less, further preferably 3.5 g·cm⁻³ or less, particularly preferably3 g·cm⁻³ or less.

A positive electrode active material layer density above these rangesmay lower the charge and discharge characteristics, particularly highcurrent density charge and discharge characteristics, because of thedifficulty permeating the nonaqueous electrolytic solution to regions inthe vicinity of the collector/active material interface. Below theseranges, the conductivity between the active materials may decrease, andbattery resistance may increase.

(2-4-2-7) Collector

The material of the positive electrode collector is not particularlylimited, and any known material may be used. Specific examples includemetallic materials such as aluminum, stainless steel, nickel plate,titanium, and tantalum; and carbonaceous materials such as carbon cloth,and carbon paper. Metallic materials are preferred, and aluminum isparticularly preferred.

In the case of metallic material, the collector may have a form of, forexample, a metal foil, a metal column, a metal coil, a metal plate, ametallic thin film, an expended metal, a punched metal, and a metalfoam. In the case of carbonaceous material, the collector may have aform of, for example, a carbon plate, a carbon thin film, and a carboncolumn. Preferred is a form of a metallic thin film. The thin film maybe meshed, as appropriate.

The collector may have any thickness, and is typically 1 μm or more,preferably 3 μm or more, further preferably 5 μm or more, and typically1 mm or less, preferably 100 μm or less, further preferably 50 μm orless. A thin film thinner than these ranges may fail to provide asufficient strength as a collector. Ease of handling may be lost with athin film thicker than the foregoing ranges.

<2-5. Separator>

A separator is typically interposed between the positive electrode andthe negative electrode to prevent shorting. In this case, the nonaqueouselectrolytic solution of the present invention is typically used bybeing impregnated in the separator.

The material and shape of the separator are not particularly limited,and any known materials and shapes may be used, provided that they arenot detrimental to the advantages of the present invention. For example,a resin, a glass fiber, and an inorganic product formed of a stablematerial against the nonaqueous electrolytic solution of the presentinvention are used, and products having a form of a porous sheet or anonwoven fabric with excellent liquid retention are preferably used.

Examples of the materials of the resin separator and the and glass fiberseparator include polyolefins (such as polyethylene, and polypropylene),polytetrafluoroethylene, polyethersulfone, and a glass filter. A glassfilter and polyolefin are preferred, and polyolefin is furtherpreferred. These materials may be used alone, or two or more may be usedin any combination and proportion.

The separator may have any thickness, and is typically 1 μm or more,preferably 5 μm or more, further preferably 10 μm or more, and typically50 μm or less, preferably 40 μm or less, further preferably 30 μm orless. With a separator thickness below these ranges, insulation andmechanical strength may suffer. Above these ranges, battery performancesuch as rate characteristics, and the energy density of the nonaqueouselectrolytic solution secondary battery as a whole may decrease.

When a porous products such as a porous sheet and a nonwoven fabric isused as the separator, the separator may have any percentage of thepores, and the percentage pore is typically 20% or more, preferably 35%or more, further preferably 45% or more, and typically 90% or less,preferably 85% or less, further preferably 75% or less. When thepercentage pore is below these ranges, the film resistance tends toincrease, and the rate characteristics tend to suffer. Above theseranges, the mechanical strength of the separator, and insulation tend todecrease.

The separator may have any average pore size, and the average pore sizeof the separator is typically 0.5 μm or less, preferably 0.2 μm or less,and typically 0.05 μm or more. When the average pore size is above theseranges, shorting is likely to occur. Below these ranges, there are caseswhere the film resistance increases, and the rate characteristicsdecrease.

Examples of the inorganic materials include oxides such as alumina andsilicon dioxide, nitrides such as aluminum nitride and silicon nitride,and sulfates such as barium sulfate and calcium sulfate. Particulate orfibrous inorganic materials are preferably used.

The separator may have a form of a thin film, for example, such as aform of a nonwoven fabric, a woven fabric, and a microporous film. Inthe case of the thin-film separator, the separator preferably has a poresize of 0.01 to 1 μm, and a thickness of 5 to 50 μm. Aside from theindependent thin film form, the separator may be one in which acomposite porous layer containing particles of the inorganic material isformed on the surface of the positive electrode and/or negativeelectrode by using a resin binder. For example, an alumina particleswith a 90% particle size of less than 1 μm may be used to form porouslayers on the both surfaces of the positive electrode by using afluororesin binder.

<2-6. Battery Design>

[Electrode Group]

The electrode group may be a laminate structure of the positiveelectrode plate and the negative electrode plate with the separator inbetween, or a wound structure of the positive electrode plate and thenegative electrode plate with the separator in between. The volumeproportion of the electrode group in the battery (hereinafter,“electrode group occupancy”) is typically 40% or more, preferably 50% ormore, and typically 90% or less, preferably 80% or less. Batterycapacity decreases when the electrode group occupancy is below theseranges. Above these ranges, void space becomes smaller, and may causebattery components to expand or the vapor pressure of the liquidcomponent of the electrolyte to increase. The resulting inner pressureincrease may lower battery characteristics such as the repeated chargeand discharge performance, and high-temperature storage characteristics,and may activate the gas release valve provided to release the innerpressure to outside.

[Collector Structure]

The collector structure is not particularly limited. However, in orderto more effectively improve discharge characteristics with thenonaqueous electrolytic solution of the present invention, it ispreferable to have a structure with which the resistance at the wiredportions and joint portions can be reduced. By reducing the internalresistance in this manner, the effect of using the nonaqueouselectrolytic solution of the present invention becomes more desirable.

When the electrode group has a laminate structure such as above, thestructure preferably involves welding of a bundle of the metal coreportions of the electrode layers to the terminal. Because the internalresistance increases when the single electrode area has a large area, itis also preferable to reduce resistance by providing a plurality ofterminals in the electrode. When the electrode group has a woundstructure, a plurality of lead structures may be provided for each ofthe positive electrode and the negative electrode, and these structuresmay be bundled to the terminal to reduce internal resistance.

[Outer Packaging Case]

The material of the outer packaging case is not particularly limited, aslong as it is a stable material against the nonaqueous electrolyticsolution to be used. Specifically, examples thereof include metals suchas nickel-plated steel plate, stainless steel, aluminum or aluminumalloys, and magnesium alloys; and laminate films of a resin and analuminum foil. Of these, in view of weight saving, a metal of aluminumor an aluminum alloy, or a laminate film is preferred.

In the outer packaging case using a metal, there may be mentioned oneforming an encapsulated sealed structure by welding metals to each otherby laser welding, resistance welding, or ultrasonic welding, or oneforming a crimped structure through a resin-made gasket using the abovemetal. In the outer packaging case using the above laminate film, theremay be mentioned one forming an encapsulated sealed structure byheat-sealing resin layers each other. For increasing sealing ability, aresin different from the resin used as the laminate film may intervenebetween the above resin layers. Particularly, in the case where theresin layers are heat-sealed through a collecting terminal to form asealed structure, the jointing is jointing of a metal with a resin, sothat a resin having a polar group or a modified resin into which a polargroup is introduced is preferably used as an intervening resin.

[Protection Device]

The protection device may be, for example, PTC (Positive TemperatureCoefficient) in which resistance increases when an abnormal heat isgenerated or an over current flows, a thermal fuse, a thermistor, avalve (current breaker valve) that shuts off the current flowing in acircuit through sharp increase of inner pressure or inner temperature ofthe battery at the time of the abnormal heat generation, or the like. Asthe above protection device, it is preferred to select one that does notact at usual use under a high current. More preferred is a design whichdoes not result in abnormal heat generation or thermal runaway even whenthe protection device is not present.

[Outer Package]

The nonaqueous electrolytic solution secondary battery of the inventionis usually composed by housing the above nonaqueous electrolyticsolution, the negative electrode, the positive electrode, the separator,and the like in an outer package. The outer package is not particularlylimited, and any known outer package may be used, provided that it isnot detrimental to the advantages of the present invention.

Specifically, usually, for example, nickel-plated iron, stainless steel,aluminum or an alloy thereof, nickel, titanium, or the like is used,though any material may be used.

The outer package may have any shape, and may be, for example,cylindrical, rectangular, laminar, coin-shaped, or large-sized.

EXAMPLES

The present invention is described below in greater detail usingExamples and Reference Examples. The present invention should not beconstrued as being limited to these Examples, unless the descriptionsbelow depart from the gist of the invention. The structures of thespecific Si compounds, the specific compounds, and the specific saltsused are referred to by the formula numbers above.

[Production of Secondary Battery]

<Production of Positive Electrode>

Ninety parts by mass of lithium nickel manganese cobalt oxide(LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂) used as positive electrode activematerial was mixed with 7 parts by mass of carbon black and 3 parts bymass of polyvinylidene fluoride, and the mixture was slurried byaddition of N-methyl-2-pyrrolidone. The slurry was evenly applied to theboth surface of a 15 μm-thick aluminum foil, dried, and pressed toproduce the positive electrode in a manner that makes the density of thepositive electrode active material layer 2.6 g·cm⁻³.

<Production of Negative Electrode>

An aqueous dispersion of carboxymethylcellulose sodium (1 mass %carboxymethylcellulose sodium) as a thickener, and an aqueous dispersionof styrene-butadiene rubber (50 mass % styrene-butadiene rubber) as abinder were added to graphite, and mixed with a disperser to form aslurry. The slurry was evenly applied to one surface of a 12 μm-thickcopper foil, dried, and pressed to produce the negative electrode in amanner that makes the density of the negative electrode active materiallayer 1.4 g·cm⁻³. The graphite had a d50 value of 10.9 μm, a specificsurface area of 3.41 m²/g, and a tap density of 0.985 g/cm³. The slurrywas produced to make the weight ratio of graphite:carboxymethylcellulosesodium:styrene-butadiene rubber 98:1:1 in the dried negative electrode.

<Production of Nonaqueous Electrolytic Solution Secondary Battery>

The positive electrode, the negative electrode, and a polyethyleneseparator were laminated in order of the negative electrode, theseparator, and the positive electrode. These battery elements werewrapped with a cylindrical aluminum laminate film, and vacuum sealedafter injecting an electrolytic solution (described later) to produce asheet-like nonaqueous electrolytic solution secondary battery. Forimproved adhesion between the electrodes, the sheet-like battery waspressurized between glass plates.

[Battery Evaluation]

<Initial Charge and Discharge Test>

In a 25° C. constant-temperature bath, the sheet-like nonaqueouselectrolytic solution secondary battery was charged at 0.05 C for 10hours, and, after a 6-hour rest period, charged to 4.1 V under 0.2 Cconstant current. After a 6-hour rest period, the battery was charged to4.1 V under 0.2 C constant current-constant voltage, and discharged to3.0 V under ⅓ C constant current. This was followed by two charge anddischarge cycles of ⅓ C constant current-constant voltage charging to4.1 V, and ⅓ C constant current discharge to 3.0 V. After ⅓ C constantcurrent-constant voltage charging to 4.1 V, the battery was stored at60° C. for 12 hours to stabilize. This was followed by five charge anddischarge cycles of ⅓ C constant current-constant voltage charging to4.1 V, and ⅓ C constant current discharge to 3.0 V at 25° C. The finaldischarge capacity was taken as initial capacity. Note that 1 C is thecurrent value with which the total battery capacity discharges in 1hour.

<Low-Temperature Discharge Characteristic Evaluation Test>

A battery charged to an electrical quantity equivalent of 50% initialcapacity (hereinafter, this state of battery is also referred to as SOC50%) was discharged at 0.3 C, 0.5 C, 1.0 C, 1.5 C, 2.0 C, and 2.5 Cunder a −30° C. environment, and the voltage after 2 seconds wasmeasured. From the current-voltage curve obtained, the current value at3 V was calculated, and the product of this current value and 3 V wastaken as the initial low-temperature discharge characteristic.

<Cycle Characteristic Evaluation Test>

A battery after initial charge and discharge was subjected to 500 chargeand discharge cycles of charging to 4.1 V under 2 C constant current,and discharge to 3.0 V under 1 C constant current at 60° C. Theproportion of the discharge capacity after 500 cycles with respect thefirst cycle discharge capacity was taken as the cycle characteristic.

<Low-Temperature Discharge Characteristic Evaluation Test after 500Cycles>

The battery after 500 cycles was adjusted to a voltage equivalent of SOC50% of the initial capacity. The battery was then discharged at 0.3 C,0.5 C, 1.0 C, 1.5 C, 2.0 C, and 2.5 C under a −30° C. environment, andthe voltage after 2 seconds was measured. From the current-voltage curveobtained, the current value at 3 V was calculated, and the product ofthis current value and 3 V was taken as the post-cycle low-temperaturedischarge characteristic.

Example 1-1

Sufficiently dried LiPF₆ was dissolved in a mixture of ethylenecarbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio3:3:4) under dry argon atmosphere in 1 mol/L of the total amount of thenonaqueous electrolytic solution (the electrolytic solution is alsoreferred to as “reference electrolytic solution”). A specific Sicompound (a) and a compound (B3) were added to the referenceelectrolytic solution in 0.5 mass % each with respect to the totalamount of the nonaqueous electrolytic solution. The nonaqueouselectrolytic solution so prepared was used to produce a battery usingthe foregoing methods, and the battery was measured for initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 10-1.

Example 1-2

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B5) was added to the electrolytic solutionin 0.2 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-3

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B9) was added to the electrolytic solutionin 0.5 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-4

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B10) was added to the electrolytic solutionin 0.5 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-5

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B11) was added to the electrolytic solutionin 0.5 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-6

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B44) was added to the electrolytic solutionin 0.5 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-7

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (B36) was added to the electrolytic solutionin 0.5 mass % instead of compound (B3). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-8

An electrolytic solution was produced in the same manner as in Example1-1, except that a compound (j) was added to the electrolytic solutionin 1.0 mass % instead of compound (a). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Example 1-9

An electrolytic solution was produced in the same manner as in Example1-3, except that a compound (j) was added to the electrolytic solutionin 1.0 mass % instead of compound (a). A battery was produced in thesame manner as in Example 1-1, and was evaluated with respect to initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The results arepresented in Table 1 as ratios with respect to the results obtained inReference Example 1-10.

Reference Example 1-1

An electrolytic solution was produced in the same manner as in Example1-1, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-2

An electrolytic solution was produced in the same manner as in Example1-2, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-3

An electrolytic solution was produced in the same manner as in Example1-3, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-4

An electrolytic solution was produced in the same manner as in Example1-4, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-5

An electrolytic solution was produced in the same manner as in Example1-5, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-6

An electrolytic solution was produced in the same manner as in Example1-6, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-7

An electrolytic solution was produced in the same manner as in Example1-7, except that compound (a) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-8

An electrolytic solution was produced in the same manner as in Example1-1, except that compound (B3) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-9

An electrolytic solution was produced in the same manner as in Example1-8, except that compound (B3) was not added to the electrolyticsolution. A battery was produced in the same manner as in Example 1-1,and was evaluated with respect to initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic. The results are presented in Table 1 as ratioswith respect to the results obtained in Reference Example 1-10.

Reference Example 1-10

By using the reference electrolytic solution, a battery was produced inthe same manner as in Example 1-1, and measured for initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic. The initiallow-temperature discharge characteristic, and the cycle characteristicwere taken as 1.00. The post-cycle low-temperature dischargecharacteristic is presented as a ratio with respect to the initiallow-temperature discharge characteristic.

TABLE 1 Initial low- Post-cycle low- temperature temperature dischargeCycle discharge Specific Si Specific characteristic characteristiccharacteristic compound compound ratio ratio ratio Ex. 1-1 (a) B3(VC)0.99 1.02 0.86 Ex. 1-2 (a) B5(EEC) 0.93 1.02 0.81 Ex. 1-3 (a) B9(LiBOB)0.88 1.02 1.04 Ex. 1-4 (a) B10(LiF₄OP) 0.93 1.01 1.15 Ex. 1-5 (a)B11(LiF₂OP) 1.08 1.03 1.14 Ex. 1-6 (a) B44(HMDI) 0.72 1.05 0.82 Ex. 1-7(a) B36(MeFSO₃) 1.11 0.97 0.97 Ex. 1-8 (j) B3(VC) 1.05 1.02 0.85 Ex. 1-9(j) B9(LiBOB) 1.08 1.01 1.02 Ref. Ex. 1-1 — B3(VC) 0.95 1.02 0.77 Ref.Ex. 1-2 — B5(EEC) 0.88 1.01 0.69 Ref. Ex. 1-3 — B9(LiBOB) 0.83 1.01 0.95Ref. Ex. 1-4 — B10(LiF₄OP) 0.93 1.01 1.01 Ref. Ex. 1-5 — B11(LiF₂OP)1.03 1.01 0.89 Ref. Ex. 1-6 — B44(HMDI) 0.64 1.04 0.78 Ref. Ex. 1-7 —B36(MeFSO₃) 0.98 0.55 0.72 Ref. Ex. 1-8 (a) — 1.07 0.97 0.97 Ref. Ex.1-9 (j) — 1.05 0.97 0.97 Ref. Ex. 1-10 — — 1.00 1.00 0.79

Typically, a system containing an additive that cannot maintain cyclecharacteristics often fails to provide sufficient effects even withadditives that improve cycle characteristics. However, it was found thatthe low-temperature discharge characteristic can greatly improve whilemaintaining the cycle characteristic improving effect of an additive(compound (B3)) by the specific combinations of the present invention,specifically by addition of the specific Si compounds of the presentinvention, as represented by compounds (a) and (j), to the electrolyticsolution that contains the cycle characteristic improving additive asrepresented by compound (B3), as can be seen in Examples 1-1 and 1-8 inTable 1.

Reference Example 1-11

An electrolytic solution was produced in the same manner as in Example1-1, except that 1,2-divinyltetramethyldisilane was added to theelectrolytic solution in 1.0 mass % instead of compound (a). A batterywas produced in the same manner as in Example 1-1, and was evaluatedwith respect to initial low-temperature discharge characteristic, cyclecharacteristic, and post-cycle low-temperature discharge characteristic.The results are presented in Table 2 as ratios with respect to theresults obtained in Reference Example 1-10.

Reference Example 1-12

An electrolytic solution was produced in the same manner as in ReferenceExample 1-11, except that compound (B3) was not added to theelectrolytic solution. A battery was produced in the same manner as inExample 1-1, and was evaluated with respect to initial low-temperaturedischarge characteristic, cycle characteristic, and post-cyclelow-temperature discharge characteristic. The results are presented inTable 2 as ratios with respect to the results obtained in ReferenceExample 1-10.

TABLE 2 Initial low- Post-cycle low- temperature temperature dischargeCycle discharge Si compound other than Specific characteristiccharacteristic characteristic specific Si compound compound ratio ratioratio Ref. Ex. 1,2- B3 (VC) 0.70 1.00 0.72 1-11divinyltetramethyldisilane Ref. Ex. 1,2- — 0.87 1.00 0.89 1-12divinyltetramethyldisilane

As can be seen in Table 2, addition of 1,2-divinyltetramethyldisilanerepresenting a Si compound other than the specific Si compound of thepresent invention tends to further lower the low-temperature dischargecharacteristic when used in combination with the specific compound ofthe present invention.

This is considered to be due to the increased resistance of the coatingformed in excess by the easy progression of self-polymerizationfacilitated by the high self-polymerizing ability of the unsaturatedbond-containing aliphatic substituent of the Si—Si compound asrepresented by 1,2-divinyltetramethyldisilane.

Using the specific Si compound of the present invention in combinationwith the specific compound improved the cycle characteristic moreeffectively than when the specific compound was added alone, as shown inExamples 1-2, 1-3, and 1-6 in Table 1. The same results were observed inExamples 1-10 and 1-11 below.

Example 1-10

An electrolytic solution was produced in the same manner as in Example1-1, except that compound (k) was added to the electrolytic solution in0.5 mass % instead of compound (a). A battery was produced, andevaluated for cycle characteristic in the same manner as in Example 1-1.The result is presented in Table 3 as a ratio with respect to the resultobtained in Reference Example 1-10.

Example 1-11

An electrolytic solution was produced in the same manner as in Example1-2, except that compound (k) was added to the electrolytic solution in0.5 mass % instead of compound (a). A battery was produced, andevaluated for cycle characteristic in the same manner as in Example 1-1.The result is presented in Table 3 as a ratio with respect to the resultobtained in Reference Example 1-10.

Reference Example 1-13

An electrolytic solution was produced in the same manner as in Example1-10, except that compound (B3) was not added to the electrolyticsolution. A battery was produced, and evaluated for cycle characteristicin the same manner as in Example 1-1. The result is presented in Table 3as a ratio with respect to the result obtained in Reference Example1-10.

TABLE 3 Cycle Specific Si Specific characteristic compound compoundratio Ex. 1-10 (k) B3 (VC)  1.04 Ex. 1-11 (k) B5 (EEC) 1.03 Ref. Ex. (k)— 1.01 1-13

As can be seen in Table 3, the phenomena observed in Examples 1-2, 1-3,and 1-6 were also observed in Examples 1-10 and 1-11 in which thespecific Si compound (k) was used. Specifically, the use the specific Sicompound of the present invention in combination with the specificcompound improved the cycle characteristic more than when thesecompounds were used alone or when neither was contained. The extent ofimprovement was more than a simple addition of the effect of eachcompound. This is believed to be due to the formation of a qualitycoating by the mixing of the coatings derived from the specific Sicompound and the specific compound, different from the coating formed byeach of these compound.

Example 1-12

An electrolytic solution was produced in the same manner as in Example1-1, except that monofluoroethylene carbonate was added to theelectrolytic solution in 0.5 mass % instead of compound (B3). A batterywas produced, and evaluated for initial low-temperature dischargecharacteristic, cycle characteristic, and post-cycle low-temperaturedischarge characteristic in the same manner as in Example 1-1. Theresults are presented in Table 4 as ratios with respect to the resultsobtained in Reference Example 1-10.

Example 1-13

An electrolytic solution was produced in the same manner as in Example1-12, except that compound (j) was added to the electrolytic solution in1.0 mass % instead of compound (a). A battery was produced, andevaluated for initial low-temperature discharge characteristic, cyclecharacteristic, and post-cycle low-temperature discharge characteristicin the same manner as in Example 1-1. The results are presented in Table4 as ratios with respect to the results obtained in Reference Example1-10.

Reference Example 1-14 Production of Positive Electrode

Lithium cobalt oxide (LiCoO₂; positive electrode active material; 94mass %), acetylene black (conductive material; 3 mass %), andpolyvinylidene fluoride (PVdF; binder; 3 mass %) were mixed in anN-methylpyrrolidone solvent, and slurried. The slurry was applied to theboth surfaces of a 15 μm-thick aluminum foil in 90% of the negativeelectrode by volume. The whole was press rolled in a thickness of 85 μmusing a press, and cut into a size of the active material layer (a widthof 65 mm, and a length of 150 mm). This was cut into an active materialwidth of 30 mm and length of 40 mm to obtain the positive electrode. Thepositive electrode was used after being dried under reduced pressure at80 degrees Celsius for 12 hours.

[Production of Negative Electrode]

Non-carbon materials silicon (73.2 parts by weight) and copper (8.1parts by weight), and an artificial graphite powder (KS-6; Timcal; 12.2parts by weight) were used as negative electrode active materials. AnN-methylpyrrolidone solution (54.2 parts by weight) containing 12 partsby weight of polyvinylidene fluoride (poly(vinylidene fluoride);hereinafter, “PVDF”), and N-methylpyrrolidone (50 parts by weight) wereadded to the negative electrode active materials, and mixed with adisperser to form a slurry. The slurry was evenly applied to a negativeelectrode collector copper foil having a thickness of 18 μm to prepare anegative electrode. The whole was pressed to make the electrode densityabout 1.5 g·cm⁻³, and cut into an active material size (a width of 30mm, and a length of 40 mm) to obtain a negative electrode (silicon alloynegative electrode). The negative electrode was used after being driedunder reduced pressure at 60 degrees Celsius for 12 hours. Forconvenience, the notation “Si” is used in Table 4.

[Production of Electrolytic Solution]

Sufficiently dried LiPF₆ was dissolved in a mixture ofmonofluoroethylene carbonate and diethyl carbonate (volume ratio 2:8)under dry argon atmosphere in 1 mol/L. Compound (a) was added to thesolution in 0.5 mass % to prepare a nonaqueous electrolytic solution.The nonaqueous electrolytic solution so prepared was used to produce abattery using the foregoing methods, and the battery was measured forinitial low-temperature discharge characteristic, cycle characteristic,and post-cycle low-temperature discharge characteristic. The results arepresented in Table 4 as ratios with respect to the results obtained inReference Example 1-16.

Reference Example 1-15

An electrolytic solution was produced in the same manner as in Example1-12, except that compound (a) was not added to the electrolyticsolution. A battery was produced, and evaluated for initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic in the same manneras in Example 1-1. The results are presented in Table 4 as ratios withrespect to the results obtained in Reference Example 1-10.

Reference Example 1-16

An electrolytic solution was produced in the same manner as in ReferenceExample 1-14, except that compound (a) was not added to the electrolyticsolution. A battery was produced, and evaluated for initiallow-temperature discharge characteristic, cycle characteristic, andpost-cycle low-temperature discharge characteristic in the same manneras in Reference Example 1-14. The initial low-temperature dischargecharacteristic, and the cycle characteristic were taken as 1.00. Thepost-cycle low-temperature discharge characteristic is presented as aratio with respect to the initial low-temperature dischargecharacteristic.

TABLE 4 Initial low- Post-cycle low- temperature temperature dischargeCycle discharge Negative Specific Si Specific characteristiccharacteristic characteristic electrode compound compound ratio ratioratio Ex. 1-12 Carbon (a) Monofluoroethylene 1.05 1.01 0.91 carbonateEx. 1-13 Carbon (j) Monofluoroethylene 1.10 1.01 0.91 carbonate Ref. Ex.Si (a) Monofluoroethylene 1.00 0.88 0.81 1-14 carbonate Ref. Ex. Carbon— Monofluoroethylene 1.04 1.01 0.87 1-15 carbonate Ref. Ex. Si —Monofluoroethylene 1.00 1.00 1.00 1-16 carbonate

As can be seen in Table 4, characteristics improved only when thecarbonaceous material was used for the negative electrode.Characteristics did not improve when the negative electrode was Si-basedmaterial (Reference Example 1-14), even when the specific Si compound ofthe present invention, and a carbonate ester having a halogen atom asrepresented by monofluoroethylene carbonate were contained.

Example 2-1

[Production of Secondary Battery]

<Production of Positive Electrode>

Ninety parts by mass of lithium nickel manganese cobalt oxide(LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂) used as positive electrode activematerial was mixed with 7 parts by mass of carbon black and 3 parts bymass of polyvinylidene fluoride, and the mixture was slurried byaddition of N-methyl-2-pyrrolidone. The slurry was evenly applied to theboth surface of a 15 μm-thick aluminum foil, dried, and pressed toproduce the positive electrode in a manner that makes the density of thepositive electrode active material layer 2.6 g·cm⁻³.

<Production of Negative Electrode>

An aqueous dispersion of carboxymethylcellulose sodium (1 mass %carboxymethylcellulose sodium) as a thickener, and an aqueous dispersionof styrene-butadiene rubber (50 mass % styrene-butadiene rubber) as abinder were added to graphite, and mixed with a disperser to form aslurry. The slurry was evenly applied to one surface of a 12 μm-thickcopper foil, dried, and pressed to produce the negative electrode in amanner that makes the density of the negative electrode active materiallayer 1.4 g·cm⁻³. The graphite had a d50 value of 10.9 μm, a specificsurface area of 3.41 m²/g, and a tap density of 0.985 g/cm³. The slurrywas produced to make the weight ratio of graphite:carboxymethylcellulosesodium:styrene-butadiene rubber 98:1:1 in the dried negative electrode.

<Production of Nonaqueous Electrolytic Solution Secondary Battery>

The positive electrode, the negative electrode, and a polyethyleneseparator were laminated in order of the negative electrode, theseparator, and the positive electrode. These battery elements werewrapped with a cylindrical aluminum laminate film, and vacuum sealedafter injecting an electrolytic solution (described later) to produce asheet-like nonaqueous electrolytic solution secondary battery. Forimproved adhesion between the electrodes, the sheet-like battery waspressurized between glass plates.

[Battery Evaluation]

<Initial Charge and Discharge Test>

In a 25° C. constant-temperature bath, the sheet-like nonaqueouselectrolytic solution secondary battery was charged at 0.05 C for 10hours, and, after a 6-hour rest period, charged to 4.1 V under 0.2 Cconstant current. After a 6-hour rest period, the battery was charged to4.1 V under 0.2 C constant current-constant voltage, and discharged to3.0 V ⅓ C under constant current. This was followed by two charge anddischarge cycles of ⅓ C constant current-constant voltage charging to4.1 V, and ⅓ C constant current discharge to 3.0 V. After ⅓ C constantcurrent-constant voltage charging to 4.1 V, the battery was stored at60° C. for 12 hours to stabilize. This was followed by five charge anddischarge cycles of ⅓ C constant current-constant voltage charging to4.1 V, and ⅓ C constant current discharge to 3.0 V at 25° C. The finaldischarge capacity was taken as initial capacity. Note that 1 C is thecurrent value with which the total battery capacity discharges in 1hour.

<Low-Temperature Discharge Characteristic Evaluation Test>

A battery charged to an electrical quantity equivalent of 50% initialcapacity (hereinafter, this state of battery is also referred to as SOC50%) was discharged at 0.3 C, 0.5 C, 1.0 C, 1.5 C, 2.0 C, and 2.5 Cunder a −30° C. environment, and the voltage after 2 seconds wasmeasured. From the current-voltage curve obtained, the current value at3 V was calculated, and the product of this current value and 3 V wastaken as the initial low-temperature discharge characteristic.

Example 2-1

Sufficiently dried LiPF₆ was dissolved in a mixture of ethylenecarbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio3:3:4) under dry argon atmosphere in 1 mol/L of the total amount of thenonaqueous electrolytic solution (the electrolytic solution is alsoreferred to as “reference electrolytic solution”). A compound (a) and acompound (B47) were added to the reference electrolytic solution in 0.5mass % each to prepare a nonaqueous electrolytic solution. Thenonaqueous electrolytic solution so prepared was used to produce abattery using the foregoing methods, and the battery was measured forlow-temperature discharge characteristic. The result is presented inTable 5 as a ratio with respect to the result obtained in ReferenceExample 2-6.

Example 2-2

An electrolytic solution was produced in the same manner as in Example2-1, except that compound (B48) was added to the electrolytic solutionin 2.0 mass % instead of compound (B47). A battery was produced, andevaluated for low-temperature discharge characteristic in the samemanner as in Example 2-1. The result is presented in Table 5 as a ratiowith respect to the result obtained in Reference Example 2-6.

Example 2-3

An electrolytic solution was produced in the same manner as in Example2-1, except that compound (B49) was added to the electrolytic solutionin 0.5 mass % instead of compound (B47). A battery was produced, andevaluated for low-temperature discharge characteristic in the samemanner as in Example 2-1. The result is presented in Table 5 as a ratiowith respect to the result obtained in Reference Example 2-6.

Example 2-4

An electrolytic solution was produced in the same manner as in Example2-1, except that compound (j) was added to the electrolytic solution in1.0 mass % instead of compound (a). A battery was produced, andevaluated for low-temperature discharge characteristic in the samemanner as in Example 2-1. The result is presented in Table 5 as a ratiowith respect to the result obtained in Reference Example 2-6.

Example 2-5

An electrolytic solution was produced in the same manner as in Example2-4, except that compound (B49) was added to the electrolytic solutionin 0.5 mass % instead of compound (B47). A battery was produced, andevaluated for low-temperature discharge characteristic in the samemanner as in Example 2-1. The result is presented in Table 5 as a ratiowith respect to the result obtained in Reference Example 2-6.

Reference Example 2-1

An electrolytic solution was produced in the same manner as in Example2-1, except that compound (B47) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 5 as a ratio with respect to the resultobtained in Reference Example 2-6.

Reference Example 2-2

An electrolytic solution was produced in the same manner as in Example2-4, except that compound (B47) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 5 as a ratio with respect to the resultobtained in Reference Example 2-6.

Reference Example 2-3

An electrolytic solution was produced in the same manner as in Example2-1, except that compound (a) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 5 as a ratio with respect to the resultobtained in Reference Example 2-6.

Reference Example 2-4

An electrolytic solution was produced in the same manner as in Example2-2, except that compound (a) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 5 as a ratio with respect to the resultobtained in Reference Example 2-6.

Reference Example 2-5

An electrolytic solution was produced in the same manner as in Example2-3, except that compound (a) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 5 as a ratio with respect to the resultobtained in Reference Example 2-6.

Reference Example 2-6

A battery was produced, and evaluated for low-temperature dischargecharacteristic in the same manner as in Example 2-1, using the referenceelectrolytic solution. The low-temperature discharge characteristic wastaken as 1.00, as presented in Table 5.

TABLE 5 Low-temperature discharge Specific Si Specific characteristiccompound salt ratio Ex. 2-1 (a) B47 1.30 Ex. 2-2 (a) B48 1.19 Ex. 2-3(a) B49 1.13 Ex. 2-4 (j) B47 1.26 Ex. 2-5 (j) B49 1.17 Ref. Ex. 2-1 (a)— 1.07 Ref. Ex. 2-2 (j) — 1.05 Ref. Ex. 2-3 — B47 1.13 Ref. Ex. 2-4 —B48 1.07 Ref. Ex. 2-5 — B49 1.02 Ref. Ex. 2-6 — — 1.00

As can be seen in Reference Examples 2-1 to 2-5 in Table 5, it was foundthat the low-temperature discharge characteristic can improve by addingthe specific Si compounds of the present invention, as represented bycompounds (a) and (j), and the specific salts of the present invention,as represented by compounds (B47) to (B49). It was also found that thelow-temperature discharge characteristic improved not by the simpleaddition of the effect of each compound, but by the specific synergy ofthese compounds, as can be seen in Examples 2-1 to 2-5.

Reference Example 2-7

An electrolytic solution was produced in the same manner as in Example2-1, except that 1,2-divinyltetramethyldisilane was added to theelectrolytic solution in 1.0 mass % instead of the compound (a). Abattery was produced, and evaluated for low-temperature dischargecharacteristic in the same manner as in Example 2-1. The result ispresented in Table 6 as a ratio with respect to the result obtained inReference Example 2-6.

Reference Example 2-8

An electrolytic solution was produced in the same manner as in Example2-7, except that compound (B47) was not added to the electrolyticsolution. A battery was produced, and evaluated for low-temperaturedischarge characteristic in the same manner as in Example 2-1. Theresult is presented in Table 6 as a ratio with respect to the resultobtained in Reference Example 2-6.

TABLE 6 Low- temperature discharge Si compound other than Specificcharacteristic specific Si compound salt ratio Ref. 1,2- B47 1.05 Ex.2-7 divinyltetramethyldisilane Ref. 1,2- — 0.87 Ex. 2-8divinyltetramethyldisilane

As can be seen in Table 6, addition of 1,2-divinyltetramethyldisilanerepresenting a Si compound other than the specific Si compound of thepresent invention tends to lower the low-temperature dischargecharacteristic when used in combination with the specific salt of thepresent invention.

This is considered to be due to the increased resistance of the coatingformed in excess by the easy progression of self-polymerizationfacilitated by the high self-polymerizing ability of the unsaturatedbond-containing aliphatic substituent of the Si—Si compound asrepresented by 1,2-divinyltetramethyldisilane.

While the invention has been described in detail with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. The present application isbased on Japanese Patent Application No. 2011-18561 filed on Jan. 31,2011, and Japanese Patent Application No. 2011-24873 filed on Feb. 8,2011, the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The nonaqueous electrolytic solution of the present invention can beused to produce a nonaqueous electrolytic solution secondary battery ofexcellent low-temperature discharge characteristic and/or cyclecharacteristic, and can preferably be used in a wide range of fields,including the field of electronic devices, in which nonaqueouselectrolytic solution secondary batteries are used.

The nonaqueous electrolytic solution, and the nonaqueous electrolyticsolution secondary battery of the present invention are not limited to aparticular use, and can be used in a variety of known applications.Specific examples include laptop personal computers, stylus-operatedpersonal computers, mobile personal computers, electronic book players,cell phones, portable facsimiles, portable copiers, portable printers,headphone stereos, video movies, liquid crystal televisions, handycleaners, portable CDs, minidiscs, transceivers, electronic organizers,calculators, memory cards, portable tape recorders, radios, back-uppower supplies, motors, automobiles, bikes, small motor vehicles,bicycles, illuminations, toys, gaming machines, watches, electric powertools, strobe lights, and cameras.

The invention claimed is:
 1. A nonaqueous electrolytic solution suitablefor use in a nonaqueous electrolytic solution secondary battery thatcomprises a negative electrode and a positive electrode capable ofstoring and releasing metal ions, and the nonaqueous electrolyticsolution, the nonaqueous electrolytic solution comprising, based ontotal nonaqueous electrolytic solution weight: (A) a first compound (A)of formula (4), in a range of from 0.01 to 10 wt. %,

A¹ to A⁶ being independently H, a halogen atom, a hydrocarbon group of 1to 10 carbon atoms that may have a heteroatom, or an optionallysubstituted hydrogen silicide group of 1 to 10 silicon atoms, A¹ to A⁶optionally binding to one another to form a ring, wherein none of A¹ toA⁶ is an aliphatic substituent having an unsaturated bond; and (B) atleast one second compound, in a range of from 0.01 to 2 wt. %, thesecond compound being selected from the group consisting of adifluorophosphate, a fluorosulfonate, and an imide salt, wherein thenonaqueous electrolytic solution comprises no carbonate ester having ahalogen atom.
 2. The solution of claim 1, further comprising: a thirdcompound, having a NCO group, of formula (3),

wherein R⁵ is an organic group of 1 to 20 carbon atoms, optionallyhaving a branched structure or an aromatic group, and Q is a hydrogenatom or an NCO group.
 3. The solution of claim 1, further comprising: amonofluorophosphate.
 4. The solution of claim 1, wherein the secondcompound (B) comprises the difluorophosphate.
 5. The solution of claim1, wherein the second compound (B) comprises the fluorosulfonate.
 6. Thesolution of claim 1, wherein the second compound (B) comprises the imidesalt.
 7. The solution of claim 1, further comprising: at least onefourth compound selected from the group consisting of ethynylethylenesulfate, propynyl vinyl sulfonate, and hexamethylene diisocyanate. 8.The solution of claim 1, wherein the second compound (B) is at least onecompound selected from the group consisting of lithiumdifluorophosphate, lithium fluorosulfonate, LiN(FSO₂)₂, LiN(CF₃SO₂)₂,and LiN(C₂F₅SO₂)₂.
 9. The solution of claim 1, wherein, in the firstcompound (A) of formula (4), A¹ to A⁶ are independently H, methyl,ethyl, n-propyl, i-propyl, n-butyl, t-butyl, or phenyl.
 10. The solutionof claim 1, wherein the first compound (A) is at least one selected fromthe group consisting of hexamethyldisilane, hexaethyldisilane,1,2-diphenyltetramethyldisilane, and 1,1,2,2-tetraphenyldisilane. 11.The solution of claim 1, comprising the first compound (A) is present ina range of from 0.01 to 2.0 wt. %, based on the total nonaqueouselectrolytic solution weight.
 12. The solution of claim 1, furthercomprising: lithium monofluorophosphate.
 13. The solution of claim 1,wherein second compound (B) is


14. The solution of claim 1, wherein second compound (B) is


15. The solution of claim 1, wherein second compound (B) is


16. The solution of claim 1, wherein, in the first compound (A) offormula (4), A¹ to A⁶ are independently H, methyl, ethyl, or phenyl. 17.The solution of claim 1, wherein, in the first compound (A) of formula(4), A¹ to A⁶ are independently H, methyl, or a substituted hydrogensilicide group of 1 silicon atom, wherein at least one of A¹ to A⁶ is H,wherein at least one of A¹ to A⁶ is methyl, and wherein at least one ofA¹ to A⁶ is a substituted hydrogen silicide group of 1 silicon atom. 18.The solution of claim 1, wherein the first compound (A) comprises


19. The solution of claim 18, wherein the first compound (A) has onlyone Si—Si bond.
 20. The solution of claim 1, wherein the second compound(B) comprises


21. The solution of claim 1, wherein the second compound (B) is at leastone selected from the group consisting of


22. A nonaqueous electrolytic solution secondary battery, comprising: acarbon-based negative electrode; a positive electrode capable of storingand releasing metal ions; and the nonaqueous electrolytic solution ofclaim 1.